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Global warming is the Earth's atmosphere warming.

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Global warming means the planet is warming up. Global warming does not assume mankind is to blame. Global warming is the observed increase in the average temperature of the Earth's atmosphere and oceans in recent decades and its projected continuation. Global warming models referenced by the Intergovernmental Panel on Climate Change (IPCC) predict that global temperatures may increase by 1.4 to 5.8 ºC (2.5 to 10.5 ºF) between 1990 and 2100. The uncertainty in this range results from both the difficulty of predicting the volume of future greenhouse gas emissions and uncertainty about climate sensitivity.

Global warming.
Global warming mean surface temperatures 1850 to 2006.
Global warming map.
Map of global warming: Mean surface temperature anomalies during the period 1995 to 2004 with respect to the average temperatures from 1940 to 1980.

Global average near-surface atmospheric temperature rose 0.6 ± 0.2 ºCelsius (1.1 ± 0.4 ºFahrenheit) in the 20th century. The prevailing scientific opinion on climate change is that "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations." The main cause of the human-induced component of warming is the increased atmospheric concentration of greenhouse gases (GHGs) such as carbon dioxide (CO2), which leads to warming of the surface and lower atmosphere by increasing the greenhouse effect. Greenhouse gases are released by activities such as the burning of fossil fuels, land clearing, and agriculture.

An increase in global temperatures can in turn cause other changes, including a rising sea level and changes in the amount and pattern of Precipitation. These changes may increase the frequency and intensity of extreme weather events, such as floods, droughts, heat waves, hurricanes, and tornados. Other consequences include higher or lower agricultural yields, glacier retreat, reduced summer streamflows, species extinctions and increases in the ranges of disease vectors. Warming is expected to affect the number and magnitude of these events; however, it is difficult to connect particular events to global warming. Although most studies focus on the period up to 2100, even if no further greenhouse gases were released after this date, warming (and sea level) would be expected to continue to rise since CO2 has a long average atmospheric lifetime.

Remaining scientific uncertainty comes from the exact degree of climate change expected in the future and particularly how changes will vary from region to region across the globe. A hotly contested political and public debate has yet to be resolved, regarding whether anything should be done, and what could be cost-effectively done to reduce or reverse future warming, or to deal with the expected consequences. Most national governments have signed and ratified the Kyoto Protocol aimed at combatting global warming. (See List of Kyoto Protocol signatories.)

Global warming terminology.

The term "global warming" is a specific case of the more general term "Climate change" (which can also refer to "global cooling," such as occurs during ice ages). In principle, "global warming" is neutral as to the period or causes, but in common usage, "global warming" generally refers to recent warming, and implies a human influence. However, the UNFCCC uses "climate change" for human-caused change, and "climate variability" for other changes. Some organizations use the term "anthropogenic climate change" for human-induced changes.

History of global warming.

Global warming.
Two millennia of mean surface temperatures according to different reconstructions, each smoothed on a decadal scale. The unsmoothed, annual value for 2004 is also plotted for reference.

Relative to the period 1860-1900, global temperatures on both land and sea have increased by 0.75 ºC (1.4 ºF), according to the instrumental temperature record. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 ºC/decade against 0.13 ºC/decade (Smith, 2005). Temperatures in the lower troposphere have increased between 0.12 and 0.22 ºC per decade since 1979, according to satellite temperature measurements. Over the one or two thousand years before 1850, world temperature is believed to have been relatively stable, with possibly regional fluctuations such as the Medieval Warm Period or the Little Ice Age.

Based on estimates by NASA's Goddard Institute for Space Studies, 2005 was the warmest year since reliable, widespread instrumental measurements became available in the late 1800s, exceeding the previous record set in 1998 by a few hundredths of a degree. Estimates prepared by the World Meteorological Organization and the UK Climatic Research Unit concluded that 2005 was still only the second warmest year, behind 1998.

A number of temperature records are available based on different data sets with different time frames. The longest perspective is available from various proxy records for recent millennia; see Temperature record of the past 1000 years for a discussion of these records and their differences. An approximately global instrumental record of temperature near the earth's surface begins in about 1860. Global observations of the atmosphere well above the earth's surface using data from radiosondes began shortly after World War II. satellite temperature measurements of the tropospheric temperature date from 1979. The attribution of recent climate change is clearest for the most recent period of the last 50 years, for which the most detailed data are available.

Causes of global warming. Attribution of recent climate change and scientific opinion on climate change.

Milankovitch cycles.
carbon dioxide during the last 400,000 years and the rapid rise since the Industrial Revolution; changes in the Earth's orbit around the Sun, known as Milankovitch cycles, are believed to be the pacemaker of the 100,000 year ice age cycle.

The climate system varies both through natural, "internal" processes as well as in response to variations in external "forcing" from both human and non-human causes, including solar activity, volcanic emissions, variations in the earth's orbit ("orbital forcing") and greenhouse gases. Climatologists agree that the earth has warmed recently. The detailed causes of this change remain an active field of research, but the scientific consensus identifies greenhouse gases as the primary cause of the recent warming. Outside the scientific community, however, this conclusion can be controversial.

Adding carbon dioxide (CO2) or methane (CH4) to Earth's atmosphere, with no other changes, will make the planet's surface warmer; greenhouse gases create a natural greenhouse effect without which temperatures on Earth would be an estimated 30 ºC (54 ºF) lower, and the Earth uninhabitable. It is therefore not correct to say that there is a debate between those who "believe in" and "oppose" the theory that adding carbon dioxide or methane to the Earth's atmosphere will, absent any mitigating actions or effects, result in warmer surface temperatures on Earth. Rather, the debate is about what the net effect of the addition of carbon dioxide and methane will be, when allowing for compounding or mitigating factors.

One example of an important feedback process is ice-albedo feedback. The increased CO2 in the atmosphere warms the Earth's surface and leads to melting of ice near the poles. As the ice melts, land or open water takes its place. Both land and open water are on average less reflective than ice, and thus absorb more solar radiation. This causes more warming, which in turn causes more melting, and the cycle continues.

Due to the thermal inertia of the earth's oceans and slow responses of other indirect effects, the Earth's current climate is not in equilibrium with the forcing imposed by increased greenhouse gases. Climate commitment studies indicate that, even if greenhouse gases were stabilized at present day levels, a further warming of perhaps 0.5 ºC to 1.0 ºC (0.91.8 ºF) would still occur.

Global warming: greenhouse gases in the atmosphere.

global temperature.
Plots of atmospheric carbon dioxide and global temperature during the last 650,000 years.

Greenhouse gases are transparent to shortwave radiation from the sun, the main source of heat on the Earth. However, they absorb some of the longer infrared radiation emitted by the Earth, thereby reducing radiational cooling and hence raising the temperature of the Earth. How much they warm the world by is shown in their global warming potential. The measure of the response to increased GHGs, and other anthropogenic and natural climate forcings is climate sensitivity. It is found by observational and model studies. This sensitivity is usually expressed in terms of the temperature response expected from a doubling of CO2 in the atmosphere. The current literature estimates sensitivity in the range 1.5-4.5 ºC (2.7-8.1 ºF).

The atmospheric concentrations of carbon dioxide and methane have increased by 31% and 149% respectively above pre-industrial levels since 1750. This is considerably higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores. From less direct geological evidence it is believed that carbon dioxide values this high were last attained 40 million years ago . About three-quarters of the anthropogenic (man-made) emissions of carbon dioxide to the atmosphere during the past 20 years are due to fossil fuel burning. The rest of the anthropogenic emissions are predominantly due to land-use change, especially deforestation.

The longest continuous instrumental measurement of carbon dioxide mixing ratios began in 1958 at Mauna Loa. Since then, the annually averaged value has increased monotonically by approximately 21% from the initial reading of 315 ppmv, as shown by the Keeling curve, to over 380 ppmv in 2006. The monthly CO2 measurements display small seasonal oscillations in an overall yearly uptrend; each year's maximum is reached during the northern hemisphere's late spring and declines during the northern hemisphere growing season as plants remove some CO2 from the atmosphere.

Methane, the primary constituent of natural gas, enters the atmosphere both from biological production and leaks from natural gas pipelines and other infrastructure. Some biological sources are natural, such as termites or forests, but others have been increased or created by agricultural activities such as the cultivation of rice paddies. Recent evidence indicates that methane concentrations have begun to stabilize, perhaps due to reductions in leakage from fuel transmission and storage facilities.

Future carbon dioxide levels are expected to continue rising due to ongoing fossil fuel usage. The rate of rise will depend on uncertain economic, sociological, technological, and natural developments. The IPCC Special Report on Emissions Scenarios gives a wide range of future carbon dioxide scenarios, ranging from 541 to 970 parts per million by the year 2100. Fossil fuel reserves are sufficient to reach this level and continue emissions past 2100, if coal and tar sands are extensively used.

Carbon sink ecosystems (forests and oceans) are being degraded by pollutants. Degradation of major carbon sinks results in higher atmospheric carbon dioxide levels.

greenhouse gases.
Anthropogenic emission of greenhouse gases broken down by sector for the year 2000.

Globally, the majority of anthropogenic greenhouse gas emissions arise from fuel combustion. The remainder is accounted for largely by "fugitive fuel" (fuel consumed in the production and transport of fuel) , emissions from industrial processes (excluding fuel combustion), and agriculture: these contributed 5.8%, 5.2% and 3.3% respectively in 1990. Current figures are broadly comparable. Around 17% of emissions are accounted for by the combustion of fuel for the generation of electricity. A small percentage of emissions come from natural and anthropogenic biological sources, with approximately 6.3% derived from agriculturally produced methane and nitrous oxide.

positive feedback effects, such as the expected release of methane from the melting of Permafrost peat bogs in Siberia (possibly up to 70,000 million tonnes), may lead to significant additional sources of greenhouse gas emissions. Note that the anthropogenic emissions of other pollutantsnotably sulfate aerosolsexert a cooling effect; this partially accounts for the plateau/cooling seen in the temperature record in the middle of the twentieth century, though this may also be due to intervening natural cycles.

Other hypotheses about global warming.

The extent of the scientific consensus on global warming that "most of the observed warming over the last 50 years is likely to have been attributable to human activities" has been investigated: In the journal Science in December 2004, Dr Naomi Oreskes published a study of the abstracts of the 928 refereed scientific articles in the ISI citation database identified with the keywords "global climate change" and published from 19932003. This study concluded that 75% of the 928 articles either explicitly or implicitly accepted the consensus viewthe remainder of the articles covered methods or paleoclimate and did not take any stance on recent climate change. The study did not report how many of the 928 abstracts explicitly accepted the hypothesis of human-induced warming, but none of the 928 articles surveyed accepted any other hypothesis.

In 2007, the Intergovernmental Panel on Climate Change concluded that human actions are "very likely" the cause of global warming, meaning a 90% or greater probability.

Contrasting with the consensus view, other hypotheses have been proposed to explain all or most of the observed increase in global temperatures. Some of these hypotheses include:

  • The warming is within the range of natural variation.
  • The warming is a consequence of coming out of a prior cool period, namely the Little Ice Age.
  • The warming is primarily a result of variances in solar irradiance, possibly via modulation of cloud cover. It is similar in concept to the operating principles of the Wilson cloud chamber, but on a global scale where Earth's atmosphere acts as the cloud chamber and the cosmic rays catalyze the production of cloud condensation nuclei.
  • The observed warming actually reflects the Urban Heat Island, as most readings are done in heavily populated areas which are expanding with growing population.

The solar variation theory of global warming.

Global warming solar.
Global warming: 30 years of solar variability.

Modeling studies reported in the IPCC Third Assessment Report (TAR) did not find that changes in solar forcing were needed in order to explain the climate record for the last four or five decades . These studies found that volcanic and solar forcings may account for half of the temperature variations prior to 1950, but the net effect of such natural forcings has been roughly neutral since then. In particular, the change in climate forcing from greenhouse gases since 1750 was estimated to be eight times larger than the change in forcing due to increasing solar activity over the same period.

Since the TAR, some studies (Lean et al., 2002, Wang et al., 2005) have suggested that changes in irradiance since pre-industrial times are less by a factor of 3 to 4 than in the reconstructions used in the TAR (e.g. Hoyt and Schatten, 1993, Lean, 2000.). Other researchers (e.g. Stott et al. 2003) believe that the effect of solar forcing is being underestimated and propose that solar forcing accounts for 16% or 36% of recent greenhouse warming. Others (e.g. Marsh and Svensmark 2000) have proposed that feedback from clouds or other processes enhance the direct effect of solar variation, which if true would also suggest that the effect of solar variability was being underestimated. In general the level of scientific understanding of the contribution of variations in solar irradiance to historical climate changes is "very low" .

The present level of solar activity is historically high. Solanki et al. (2004) suggest that solar activity for the last 60 to 70 years may be at its highest level in 8,000 years; Muscheler et al. disagree, suggesting that other comparably high levels of activity have occurred several times in the last few thousand years. Solanki concluded based on their analysis that there is a 92% probability that solar activity will decrease over the next 50 years. In addition, researchers at Duke University (2005) have found that 1030% of the warming over the last two decades may be due to increased solar output. In a review of existing literature, Foukal et al. (2006) determined both that the variations in solar output were too small to have contributed appreciably to global warming since the mid-1970s and that there was no evidence of a net increase in brightness during this period.

Global warming attributed and expected effects.

Global glacial mass balance in the last fifty years, reported to the WGMS and the NSIDC. The increased downward trend in the late 1980s is symptomatic of the increased rate and number of retreating glaciers.

Some effects on both the natural environment and human life are already being attributed at least in part to global warming. glacier retreat, ice shelf disruption such as of the Larsen Ice Shelf, Sea level rise, changes in rainfall patterns, increased intensity and frequency of hurricanes and extreme weather events, are being attributed at least in part to global warming. While changes are expected for overall patterns, intensity, and frequencies, it is difficult or impossible to attribute specific events (such as Hurricane Katrina) to global warming.

Some anticipated effects include Sea level rise of 110 to 770 mm by 2100, repercussions to agriculture, possible slowing of the thermohaline circulation, reductions in the ozone layer, increased intensity and frequency of hurricanes and extreme weather events, lowering of ocean pH, the spread of diseases such as malaria and dengue fever, and mass extinction events.

The extent and probability of these consequences is a matter of considerable uncertainty. A summary of probable effects and recent understanding can be found in the report of the IPCC Working Group II.

Mitigation of global warming and adaptation to global warming.

fossil fuel usage.
The Energy Information Administration predicts world energy and fossil fuel usage will rise in the next decades.

The consensus among climate scientists that global temperatures will increase has led nations, states, corporations and individuals to implement actions to try to curtail global warming. Some of the strategies that have been proposed for mitigation of global warming include development of new technologies; carbon offsets; Renewable energy such as biodiesel, wind power, and solar power; nuclear power; electric or hybrid automobiles; fuel cells; energy conservation; carbon taxes; improving natural carbon dioxide sinks; deliberate production of sulfate aerosols, which produce a cooling effect on the Earth; population control; and Carbon capture and storage. Many environmental groups encourage individual action against global warming, often aimed at the consumer, and there has been business action on climate change.

The world's primary international agreement on combating climate change is the Kyoto Protocol. The Kyoto Protocol is an amendment to the United Nations Framework Convention on Climate Change (UNFCCC). Countries that ratify this protocol commit to reduce their emissions of carbon dioxide and five other greenhouse gases, or engage in emissions trading if they maintain or increase emissions of these gases.

Climate models of global warming.

global warming climate models.
Calculations of global warming from a range of climate models under the SRES A2 emissions scenario, which assumes no action is taken to reduce emissions.
surface warming.
The geographic distribution of surface warming during the 21st century calculated by the HadCM3 climate model if a business as usual scenario is assumed for economic growth and greenhouse gas emissions. In this figure, the globally averaged warming corresponds to 3.0 ºC (5.4 ºF).

Scientists have studied global warming with computer models of the climate (see below). Before the scientific community accepts a climate model, it has to be validated against observed climate variations. As of 2006, models with sufficiently high resolution are able to successfully simulate summer and winter differences, the North Atlantic Oscillation, and El Nio. All validated current models predict that the net effect of adding greenhouse gases will be a warmer climate in the future. However, even when the same assumptions of fossil fuel consumption/CO2 emission are used, the amount of predicted warming varies between models and there still remains a considerable range of climate sensitivity predicted by the models which survive these tests; one of the most important sources of this uncertainty is believed to be different ways of handling clouds. Part of the technical summary of the IPCC TAR includes a recognition of the need to quantify this uncertainty: "In climate research and modeling, we should recognize that we are dealing with a coupled non-linear system, and therefore that the prediction of a specific future climate is not possible. Rather the focus must be on the probability distribution of the system's possible future states by the generation of ensembles of model solutions." (See, page 78.) An example of a study which aims to do this is the Climateprediction.net project; their methodology is to investigate the range of climate sensitivities predicted for the 21st century by those models which are first shown to give a reasonable simulation of late 20th century climate change.

As noted above, climate models have been used by the IPCC to anticipate a warming of 1.4 ºC to 5.8 ºC (2.5 ºF10.4 ºF) between 1990 and 2100. They have also been used to help investigate the causes of recent climate change by comparing the observed changes to those that the models predict from various natural and human derived forcing factors. In addition to having their own characteristic climate sensitivity, models have also been used to derive independent assessments of climate sensitivity.

Climate models can produce a good match to observations of global temperature changes over the last century. These models do not unambiguously attribute the warming that occurred from approximately 1910 to 1945 to either natural variation or human effects; however, they suggest that the warming since 1975 is dominated by man-made greenhouse gas emissions. Adding simulation of the carbon cycle to the models generally shows a positive feedback, though this response is uncertain (under the A2 SRES scenario, responses vary between an extra 20 and 200 ppm of CO2). Some observational studies also show a positive feedback.

Uncertainties in the representation of clouds are a dominant source of uncertainty in existing models, despite clear progress in modeling of clouds. There is also an ongoing discussion as to whether climate models are neglecting important indirect and feedback effects of solar variability. Further, all such models are limited by available computational power, so that they may overlook changes related to small-scale processes and weather (e.g. storm systems, hurricanes). However, despite these and other limitations, the IPCC considered climate models "to be suitable tools to provide useful projections of future climates".

In December, 2005 Bellouin et al. suggested in Nature that the reflectivity effect of airborne pollutants was about double that previously expected, and that therefore some global warming was being masked. If supported by further studies, this would imply that existing models under-predict future global warming.

Global warming and other related issues. Ocean acidification of global warming.

Increased atmospheric carbon dioxide increases the amount of CO2 dissolved in the oceans. Unfortunately, carbon dioxide gas dissolved in the ocean reacts with water to form carbonic acid resulting in ocean acidification. Since biosystems are adapted to a narrow range of pH this is a serious concern directly driven by increased atmospheric CO2 and not global warming.

Global warming relationship to ozone depletion.

Although they are often interlinked in the Mass media, the connection between global warming and ozone depletion is not strong. There are five areas of linkage:

  • The same carbon dioxide radiative forcing that produces near-surface global warming is expected (perhaps somewhat surprisingly) to cool the stratosphere. This, in turn, would lead to a relative increase in Ozone depletion and the frequency of ozone holes.
greenhouse gases.
radiative forcing from various greenhouse gases and other sources.
  • Conversely, ozone depletion represents a radiative forcing of the climate system. There are two opposed effects: 1) reduced ozone allows more solar radiation to penetrate, thus warming the troposphere instead of the stratosphere. 2) The resulting colder stratosphere emits less long-wave radiation down to the troposphere, thus having a cooling effect. Overall, the cooling dominates: the IPCC concludes that observed stratospheric O3 losses over the past two decades have caused a negative forcing of the surface-troposphere system of about -0.15 ± 0.10 W/m².
  • One of the strongest predictions of the greenhouse effect theory is that the stratosphere will cool. Although this cooling has been observed, it is not trivial to separate the effects of changes in the concentration of greenhouse gases and ozone depletion since both will lead to cooling. However, this can be done by numerical stratospheric modeling. Results from the NOAA Geophysical Fluid Dynamics Laboratory show that above 20 km, the greenhouse gases dominate the cooling.
  • Ozone depleting chemicals are also greenhouse gases, representing 0.34 ±0.03 W/m², or about 14% of the total radiative forcing from well-mixed greenhouse gases.
  • Decreased ozone leads to an increase in ultraviolet levels. Ultraviolet radiation may be responsible for the death of ocean algae, which operate as a carbon dioxide sink in the ocean. Increased UV, therefore, may lead to a decrease in carbon dioxide uptake, thereby raising global carbon dioxide levels.

Global warming and the relationship to global dimming.

Some scientists now consider that the effects of Global dimming (the reduction in sunlight reaching the surface of the planet, possibly due to aerosols) may have masked some of the effect of global warming. If this is so, the indirect aerosol effect is stronger than previously believed, which would imply that the climate sensitivity to greenhouse gases is also stronger.

Pre-human global warming.

The Earth has experienced natural global warming and cooling many times in the past, and can offer useful insights into present processes. It is thought by some geologists that a rapid buildup of greenhouse gases caused the Earth to experience global warming in the early Jurassic period, with average temperatures rising by 5 ºC (9.0 ºF). Research by the open university published in Geology (32: 157160, 2004) indicates that this caused the rate of rock weathering to increase by 400%. As such weathering locks away carbon in Calcite and dolomite, carbon dioxide levels dropped back to normal over roughly the next 150,000 years.

Sudden releases of methane from clathrate compounds (the Clathrate Gun Hypothesis) have been hypothesized as a cause for other past global warming events, including the Permian-Triassic extinction event and the Paleocene-Eocene Thermal Maximum. However, warming at the end of the last glacial period is thought not to be due to methane release. Instead, natural variations in the Earth's orbit (Milankovitch cycles) are believed to have triggered the retreat of ice sheets by changing the amount of solar radiation received at high latitude and led to deglaciation.

The greenhouse effect is also invoked to explain how the Earth made it out of the Snowball Earth period 600 million years ago. During this period all silicate rocks were covered by ice, thereby preventing them from combining with atmospheric carbon dioxide. The atmospheric carbon dioxide level gradually increased until it reached a level that could have been as much as 350 times the current level. At this point temperatures were raised enough to melt the ice, even though the reflective ice surfaces had been reflecting most sunlight back into space. Increased amounts of rainfall would quickly wash the carbon dioxide out of the atmosphere, and thick layers of abiotic carbonate sediment have been found on top of the glacial rocks from this period.

Using paleoclimate data for the last 500 million years Veizer et al. (2000, Nature 408, pp. 698701) concluded that long-term temperature variations are only weakly related to carbon dioxide variations. Most paleoclimatologists believe this is because other factors, such as Continental drift and mountain building have larger effects in determining very long term climate. However, Shaviv and Veizer (2003,) proposed that the biggest long-term influence on temperature is actually the Solar System's motion around the galaxy, and the ways in which this influences the atmosphere by altering the flux of cosmic rays received by the Earth. Afterwards, they argued that over geologic times a change in carbon dioxide concentrations comparable to doubling pre-industrial levels, only results in about 0.75 ºC (1.3 ºF) warming rather than the usual 1.54.5 ºC (2.78.1 ºF) reported by climate models . They acknowledge (Shaviv and Veizer 2004) however that this conclusion may only be valid on multi-million year time scales when glacial and geological feedback have had a chance to establish themselves. Rahmstorf et al. 2004 argue that Shaviv and Veizer arbitrarily tuned their data, and that their conclusions are unreliable.

Pre-industrial global warming.

Paleoclimatologist William Ruddiman has argued that human influence on the global climate began around 8,000 years ago with the start of forest clearing to provide land for agriculture and 5,000 years ago with the start of Asian rice irrigation. He contends that forest clearing explains the rise in carbon dioxide levels in the current interglacial that started 8,000 years ago, contrasting with the decline in carbon dioxide levels seen in the previous three interglacials. He further contends that the spread of rice irrigation explains the breakdown in the last 5,000 years of the correlation between the Northern Hemisphere solar radiation and global methane levels, which had been maintained over at least the last 11 22,000-year cycles. Ruddiman argues that without these effects, the Earth would be nearly 2 ºC cooler and "well on the way" to a new ice age. Ruddiman's interpretation of the historical record, with respect to the methane data, has been disputed.

Recent findings, developments on global warming. International organizations.

In February 2007, the U.N. Intergovernmental Panel on Climate Change (IPCC) released a summary report stating that it is "very likely" that climate change is caused by human activity.

The IPCC's position was a marked departure from a November 2006 statement by the World Meteorological Organization, which helped found the IPCC. The meteorological organization, after contentious debate, said it could not link past stronger storms to global warming. The debate about whether stronger hurricanes were linked to global warming was one division in the scientific community, which was otherwise largely united in agreeing that mankind is behind recent global warming.

More About Global Warming.

What If We Burn Everything?

Nov 1, 2005 - Scientists at the Lawrence Livermore National Laboratory have developed a detailed model of the Earth's climate over the next few centuries to answer the question... what if we burned all the fossil fuels by the year 2300. The answer, of course, isn't a pretty picture. In their model, global temperatures will rise 8-degrees Celsius (14.5 F), and melting polar caps will raise the oceans 7 metres (23 feet). The damage would be even worse in the polar regions, which could grow by 20-degrees C (68 F).

Early Earth Had Toxic Oceans

Oct 7, 2005 - Researchers from NASA have confirmed that it would have been impossible for advanced life forms, like fish or mammals, to live in the Earth's early oceans because it was such a toxic environment. The scientists studied ancient rock formations, and found evidence of photosynthetic bacteria living as recently as 1.6 billion years ago. This bacteria would have required both sunlight and an environment rich in hydrogen sulfide - this environment would have been quite toxic for air breathing creatures.

Number of Powerful Hurricanes Has Doubled

Sep 20, 2005 - Think there are more hurricanes these days? Well, you're right. In the last 35 years, meteorologists have recorded that the number of powerful category 4 and 5 hurricanes has doubled. In the 1970s, there were approximately 10 category 4/5 storms globally each year. In 2004 there were 18. The trend is happening because global sea temperatures have risen over the last half century. Powerful hurricanes in the North Atlantic, such as Hurricane Katrina, have increased at an even faster rate.

More Sunlight is Hitting the Earth

May 6, 2005 - The amount of sunlight reaching the Earth's surface has been on the rise for the past decade on average, potentially accelerating the effects of global warming. Scientists had been measuring a decrease in sunlight from the 1960s to the 1990s, because of rising pollution was actually blocking sunlight. With better pollution controls in place, the planet's surface has brightened by about 4% in the last 10 years.

History of the Earth's Atmosphere Written in Rocks

May 5, 2005 - Geologists have built up a suite of tools and techniques that let them peer back in time to watch the formative stages of the Earth and how it's changed over time - by looking inside rocks. By analyzing trapped water and air in rocks, geologists are studying how our atmosphere changed 3.9 billion years ago, when the crust of the planet was just forming, and there wasn't any oxygen in the air.

Low Oxygen Accelerated the Great Dying

Apr 19, 2005 - The biggest mass extinction in the Earth's history happened approximately 250 million years ago. During the "Great Dying", more than 90% of creatures in the ocean, and 75% of life on land went extinct. What caused the extinction is still up for debate, but a researcher from the University of Washington thinks that low levels of oxygen in the atmosphere sure didn't help. Oxygen went down to 12% (currently it's 21%), and this made standing at sea level the same as being atop a 5,300 metre mountain (17,000 feet).

First Global Map of Methane Emissions

Mar 18, 2005 - The European Space Agency's Envisat has completed a map of global methane emissions, and not surprisingly, areas of dense population show the highest levels of this greenhouse gas. What is a surprise, however, is that there are higher emissions than anticipated over tropical areas of the planet. This could be because of burning, termites, animals, or just increased decomposition of plants. Methane gas traps 21 times more heat per molecule than carbon dioxide, so it's important to locate these sources and limit them.

Did Clouds in Space Cause Snowball Earth?

Mar 4, 2005 - Scientists are fairly certain that the Earth went through a snowball glaciation 600-800 million years ago, when the entire planet was locked in snow and ice. One new theory to explain this extreme cooling is the possibility that the solar system passed through an interstellar cloud of dust and gas, which obscured the light from the Sun. Even if the cloud wasn't thick enough to obscure light from the Sun, it could have enabled charged particles to pass into the Earth's atmosphere and destroy the ozone layer. These clouds are huge, and it would take the solar system 500,000 years to pass through one.

Air Pollution Linked to Growth of Life in Oceans

Feb 11, 2005 - Researchers from the Georgia Institute of Technology have uncovered a surprising link between air pollution levels over land, and the growth of phytoplankton in the ocean. These tiny, but hardworking, aquatic plants carry out half the Earth's photosynthesis, and are responsible for removing tremendous quantities of carbon dioxide from the atmosphere. Normal dust storms produce iron which the phytoplankton can't use, but when it's modified by sulfur dioxide pollution, the iron becomes soluble and can trigger phytoplankton growth.

Did Volcanoes Cause the Great Dying?

Jan 21, 2005 - Something wiped out most of the life on Earth 250 million years ago. Evidence has been building that it was an asteroid or comet strike that made Earth unlivable nearly instantly. But other scientists think that it wasn't instantaneous; instead, they found fossil evidence that the extinction occurred over the course of 10 million years. A group of volcanoes in Siberia spewed out gas continuously that set off a runaway greenhouse effect. Lowered oxygen levels in the atmosphere combined with intense heat would have hit life a deadly double blow.

Worldwide Pollution Levels Seen From Space

Oct 12, 2004 - After 18 months of observations by the Envisat Earth monitoring satellite, the European Space Agency has produced a detailed image of the entire Earth that shows nitrogen dioxide pollution. Nitrogen dioxide is generally a man-made gas - produced in power plants, heavy industry, and burning - which can cause lung disease and respiratory problems. Previous maps like this have been made, but this image is at a resolution of 60 x 30 km (37 x 19 miles), so scientist can pick out individual cities which are a source of pollution.

Antarctica Is Getting Ready to Really Heat Up

Oct 7, 2004 - With all this talk of global warming, it may come as a surprise that Antarctica has actually been mostly getting colder over the last 30 years. But new research from NASA indicates that this trend is about to reverse, and the continent will warm over the next 50 years. Researchers found, ironically, that low ozone levels actually made the continent colder, but with restrictions on ozone-destroying chemicals around the planet, this cooling effect is going to go away as the ozone layer returns. If temperatures rise too high, the continent's ice sheets will melt and slide into the ocean, raising water levels around the world.

Arriving This Week: The Ozone Hole

Sep 1, 2004 - The European Space Agency's Envisat earth observation satellite is getting ready for the arrival of an annual event - the opening of the hole in the Earth's ozone layer. Since a hole first opened up in the mid-1980s, satellites have been tracking its arrival and shape for years, and scientists have gotten quite good at predicting the conditions that will create the gap. The ozone hole should open up in about a week's time, and then close up again in November or December when higher temperatures around the South Pole will mix ozone-rich air into the region.

How Deforestation in Brazil is Affecting Local Climate

Jun 9, 2004 - Satellites are giving scientists a bird's eye view of deforestation in the Brazilian rainforest, and the impact this is happening on the local environment. The researchers studied many years of data gathered by NASA's Tropical Rainfall Measuring Mission (TRMM), and found that the land heated up more quickly in the deforested areas. The increased temperatures let to more evaporation and greater rainfall during normally drier seasons. This challenges previous theories that said deforestation would lead to more arid conditions.

Riding the Pollution Train

May 3, 2004 - NASA satellites have helped scientists understand how pollution in Asia catches an express train ride on winds to travel all the way to the southern Atlantic Ocean; as much as half of pollution in the region could be from Asia. Scientists used data from two satellites and high-altitude balloons to spot the situations where near-surface smog from human pollution and natural forest fires "catches the train", and travels thousands of kilometres.

Solar Plane Will Attempt to Go Around the Earth

Mar 31, 2004 - The European Space Agency will be supplying technology to assist adventurer Bertrand Piccard's attempt to fly a solar-powered plane around the world. Piccard was part of the team that successfully flew a balloon around the Earth. The solar powered plane will have a 70-metre wingspan (larger than a Boeing 747), and carry enough batteries to be able to fly in the night as well. The plane would fly at an altitude of 10 km; well above the clouds to capture all the available sunlight. The first round-the-world attempt will be made some time after 2009.

More Details on Water Vapour Feedback

Mar 17, 2004 - New research funded by NASA indicates that some models of climate change might be overestimating what impact water vapour will have in raising average temperatures. This new study, based on data gathered by the Upper Atmosphere Research Satellite (UARS), verified that water vapour increases in the atmosphere as surface temperatures rise, but not as much as previously theorized. Water vapour is a significant greenhouse gas, so this new research will help scientists make much better predictions about future climate changes.

The Origins of Oxygen on Earth

Mar 17, 2004 - Oxygen is one of the most important elements on Earth to life, and it comprises a fifth of our atmosphere. It's a volatile element, so it can't exist in large quantities unless something, like life, is continually producing it. The mainstream view is that plants evolved oxygen photosynthesis early on, and then produced large amounts of oxygen. Another view, tested under laboratory conditions, is that when volcanic rocks weather, they release oxygen into the atmosphere. Perhaps it's a combination of these factors that built up our oxygen.

Mission Sets Out to Map Southern Glaciers

Mar 4, 2004 - An international team of scientists has set out on a three-week expedition to South America and Antarctica to survey glaciers to help determine the rate of climate change on Earth. They'll gather data using a specially configured DC-8 aircraft carrying a tool called the Airborne Synthetic Aperture Radar. It scans the ground in multiple wavelengths, polarizations, and in interferometric modes to "see" through treetops, sand and snow pack and produce topographic models.

New Ozone Hole Isn't Quite the Record

Sep 25, 2003 - The ozone hole above Antarctica is the second largest ever recorded this year, covering 28.2 million square kilometres - down slightly from the record in 2000. The observations were made by NASA's Earth Probe Total Ozone Mapping Spectrometer and the NOAA's Solar Backscatter Ultraviolet instrument, and were confirmed by balloon-carried instruments. Even through chlorofluorocarbons, which destroy the ozone in our atmosphere, were banned in 1995, they're still abundant and it'll probably take another 50 years before the ozone hole disappears completely.

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