is global warming a theory?

Question

i was just wondering? post your comments and concerns

Answer 1

In science a "theory" means an idea that is supported by a lot of evidence but has not yet been completely explained or proved. So, by that standard "global climate change" is a theory. It is also a "theory" that the change has been caused in a large part by human activity.

The recent IPCC report endorsed by thousands of scientists suggests that we have enough evidence to be "90% sure" that these theories are correct. That is a very high level of confidence, so most scientists would agree that the argument is over and the evidence for the global warming is convincing to people who are educated in these areas.

Of course, there are some people who don't believe it, but judging by their ignorant comments on Yahoo, I don't think their opinions count for much.

Answer 2

well there are alot of things in science tat are considered a theory i think hteorys have to not be diproven for 50 yrs and since we havn't known about global warming for 50 years... but there are only like 20 laws in science and i can tell you now that there is more tham 20 things in science that are true...
Don't keep your hopes up that it is false.
And to those ppl out there (sorry to be mean but some people need to open their eyes) that are saying politics is trying to convince us that we are all gona die... why would they??? It causes a problem for them two don't you think that they would rather just ignore this problem??? i mean heaps of governments are claiming that it is false so they don't have to take the blame and deal with it!!! Think people think why would they do that????

Answer 3

I believe if there is global warming it is a natural cycle that Al Gore is using as a scam.....remember he did invent the internet....at one time. I want to know why if there is global warming is it so frickin' cold here? Why is Colorado having more snow than ever, New York 6 to 14 feet snow fall, Phoenix, Az 44 degrees in January. Hawaii 54 degrees? Where is/was the global warming?

Answer 4

Yes,it's a theory that so far fits the facts.Gravity,also,is a theory that so far fits the facts.I really don't get the people that deny global warming .

Answer 5

Yes it's a theory. There are scientists that say 1 major volcano eruption emits more greenhouse gasses than humans ever have.

Answer 6

i think the UN just want to prove that they can srew with us. the want us to believe things just b/c they say so . the keep saying that they predicted gobal warming at a date too soon and they keep extends the time till it takes too. yeah we screw up nature and everyone would prefer a cleaner world but it is not a good reason to scare the crap out of us like that.

Answer 7

no it's not a theory, they have proof of green house effect and glacier meltin to ice cube.

Answer 8

lets hope so

Answer 9

Global warming is the observed increase in the average temperature of the Earth's atmosphere and oceans in recent decades and its projected continuation. Models referenced by the Intergovernmental Panel on Climate Change (IPCC) predict that global temperatures are likely to increase by 1.1 to 6.4 °C (2.0 to 11.5 °F) between 1990 and 2100.[1] The uncertainty in this range results from two factors: differing future greenhouse gas emission scenarios, and uncertainties regarding climate sensitivity.

Global average near-surface atmospheric temperature rose 0.74 ± 0.18 °Celsius (1.3 ± 0.32 °Fahrenheit) in the last 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,"[1] 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. Other phenomena such as solar variation and volcanoes have had smaller and probably negative effects 1950.[2] A small number of scientists disagree with regard to the nature of the observed warming. Svante Arrhenius first predicted CO2-induced global warming in 1896.

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 for more than a millennium, since CO2 has a long average atmospheric lifetime.

Remaining scientific uncertainties include the exact degree of climate change expected in the future, and especially how changes will vary from region to region across the globe. A hotly contested political and public debate also 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 combating global warming. (See: List of Kyoto Protocol signatories.)

Contents [hide]
1 Terminology
2 History of warming
3 Causes
3.1 Greenhouse gases in the atmosphere
3.2 Solar variation
4 Attributed and expected effects
5 Mitigation
5.1 Kyoto Protocol
6 Climate models
7 Other related issues
7.1 Ocean acidification
7.2 Relationship to ozone depletion
7.3 Relationship to global dimming
7.4 Pre-human global warming
7.5 Pre-industrial global warming
8 Notes
9 Further reading
10 See also
11 External links
11.1 Scientific
11.2 Educational
11.3 Other



Terminology
The term global warming is a specific example of the broader term climate change, which can also refer to global cooling. In principle, global warming is neutral as to the period or causes, but in common usage the term generally refers to recent warming and implies a human influence.[3] The UNFCCC uses the term "climate change" for human-caused change, and "climate variability" for other changes.[4] Some organizations use the term "anthropogenic climate change" for human-induced changes.


History of warming
Main article: Temperature record

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 °C (1.4 °F), according to the instrumental temperature record; the urban heat island is not believed to be significant. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C/decade against 0.13 °C/decade) (Smith, 2005). Temperatures in the lower troposphere have increased between 0.12 and 0.22 °C per decade since 1979, according to satellite temperature measurements. Over the one or two thousand years before 1850, 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 the second warmest year, behind 1998.[5][6]

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.

Note that the anthropogenic emissions of other pollutants—notably sulphate aerosols—exert a cooling effect; this partially accounts for the plateau/cooling seen in the temperature record in the middle of the twentieth century,[7] though this may also be due to intervening natural cycles.


Causes
Main articles: Attribution of recent climate change and Scientific opinion on climate change

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 through natural, internal processes and in response to variations in external "forcing" from both human and natural causes. These forcing factors include solar activity, volcanic emissions, variations in the earth's orbit (orbital forcing) and greenhouse gases. The detailed causes of the recent warming remain an active field of research, but the scientific consensus identifies greenhouse gases as the main influence.

Contrasting with this consensus view, other hypotheses have been proposed to explain all or most of the observed increase in global temperatures, including: 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; and the warming is primarily a result of variances in solar radiation.

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 °C (54 °F) lower, so that Earth would be uninhabitable. It is therefore not correct to say that there is a debate between those who "believe in" and "oppose" the greenhouse effect as such. Rather, the debate concerns the net effect of the addition of greenhouse gases when allowing for compounding or mitigating factors.

One example of an important feedback process is ice-albedo feedback.[8] 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 this 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 about 0.5 °C (0.9 °F) would still occur.[9]


Greenhouse gases in the atmosphere
Main article: Greenhouse effect

Recent increases in atmospheric CO2. 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.The measure of the response to increased greenhouse gas concentrations and other anthropogenic and natural climate forcings is climate sensitivity. It is found by observational and model studies.[10] 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 of 1.5 to 4.5 °C (2.7 to 8.1 °F).

The major natural greenhouse gases are water vapor, which causes about 36-70% of the greenhouse effect on Earth (not including clouds); carbon dioxide, which causes 9-26%; methane, which causes 4-9%, and ozone, which causes 3-7%.

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.[citation needed] 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.[11]

Future carbon dioxide levels are expected to rise due to ongoing burning of fossil fuels. The rate of rise will depend on uncertain economic, sociological, technological, natural developments, but may be ultimately limited by the availability of fossil fuels. The IPCC Special Report on Emissions Scenarios gives a wide range of future carbon dioxide scenarios,[12] 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, tar sands or Methane clathrates are extensively used.[citation needed]Carbon sink ecosystems (forests and oceans)[13] are being degraded by pollutants.[14] Degradation of major carbon sinks results in higher atmospheric carbon dioxide levels.


Anthropogenic emission of greenhouse gases broken down by sector for the year 2000.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[15] not included in IPCC's climate models.[citation needed]


Solar variation
Main article: Solar variation
Modeling studies reported in the IPCC Third Assessment Report (TAR) 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.[16] The IPCC Fourth Assessment Report (AR4) gives a best estimate for radiative forcing from changes in solar activity of +0.12 watts per square metre. This is less than half of the estimate given in the TAR. For comparison, the combined effects of all human activity are estimated to be an order of magnitude greater at +1.6 watts per square meter.[1]

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.[17]

Some scientists assert that a warming of the stratosphere, which has not been observed, would be expected if there were a significant increase in solar activity.[18]

Some researchers (e.g. Stott et al. 2003)[19] 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)[20] 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 IPCC describes the level of scientific understanding of the contribution of variations in solar irradiance to historical climate changes as "low."[1]


400 year history of sunspot numbers.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.[21] 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 10–30% of the warming over the last two decades may be due to increased solar output.[22]


Attributed and expected effects

Global glacial mass balance in the last 50 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.Main article: Effects of global warming
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 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,[23] 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.[1]


Mitigation
Main articles: Mitigation of global warming and Adaptation to global warming
The consensus among climate scientists that global temperatures will continue to 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; carbon capture and storage; and nanotechnology. Many environmental groups encourage individual action against global warming, often aimed at the consumer, and there has been business action on climate change.


Kyoto Protocol
Main article: Kyoto Protocol
The world's primary international agreement on combating global warming 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. Developing countries are exempt from meeting emission standards in Kyoto. This includes China and India, the second and third largest emitters of CO2, behind the United States.


Climate models
Main article: Global climate model

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.
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 °C (5.4 °F)Scientists have studied global warming with computer models of the climate. These 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 and CO2 emission are used, the amount of predicted warming varies between models and there still remains a considerable range of climate sensitivity.

Including model and future greenhouse gas uncertainty, the IPCC anticipates a warming of 1.1 °C to 6.4 °C (2.0 °F to 11.5 °F) 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.

Climate models can produce a good match to observations of global temperature changes over the last century [2]. 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.

Most global climate models, when run to predict future climate, are forced by imposed greenhouse gas scenarios, generally one from the IPCC Special Report on Emissions Scenarios (SRES). Less commonly, models may be run by adding a simulation of the carbon cycle; this 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.[3]

The representation of clouds is one of the main sources of uncertainty in present-generation models, though progress is being made on this problem.[4] There is also an ongoing discussion as to whether climate models are neglecting important indirect and feedback effects of solar variability.