In 1988, the Intergovernmental Panel on Climate Change was established to assess scientific, technical, and socioeconomic information relating to the world's climate change. In 2007, the IPCC clearly stated that "Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level." Later sections can be found in the following link: http://www.ipcc.ch/. Other reports released in 2006 include http://www.hm-treasury.gov.uk/independant_reviews/stern_review_economics_climate_change/sternreview_index.cfm.
Almost all of the few remaining critics of the reality of climate change are employed or funded by industries and nations that taking action would impact them financially.
Human and Natural Drivers of Climate Change
Global atmospheric concentrations of carbon dioxide, nitrous oxide and methane have increased substantially as a result of human activity since 1750. These measurements are taken from ice cores ranging back thousands of years. The carbon dioxide is due to burning of fossil fuels and land-use changes, while the release of methane and nitrous oxide is directly realted to agriculture.
Carbon Dioxide is the most important anthropogenic greenhouse gas. In 2005 the global atmospheric concentration was the highest in 650,000 years and in the past 10 years the concentration has been the highest since the beginning of the measurements in 1960.
The primary source of increased CO2 levels has been fossil fuel combustion, the land-use change issue is significant but a smaller contribution. Estimates of Carbon dioxide emissions concentration have a large uncertainty.
Methane has also peaked in 2005 for its global atmospheric concentration, which exceeds by far the measurements from ice cores of the last 650,000 years prior. It is very likely that the growth of methane concentration is due to to anthropogenic activities superiorily from agriculture and fossil fuel use.
Nitrous Oxide atmospheric concentration has increased from pre-industrial value and has continued to grow at a constant rate since 1980. More than a third of Nitrous Oxide emissions are anthropogenic and primarily due to agriculture.
The understanding of anthropogenic warming and cooling influences on climate has improved to a very high confidence level.
- The carbon dioxide radiative forcing has had the largest change for any decade in at least 200 years.
- Anthropogenic contributions of aerosols (primarily sulphate, organic carbon, black carbon, nitrate and dust) all together produced a cooling effect. Aerosols affect radiative forcing, cloud albedo, as well as cloud lifetime and precipitation.
Direct Observations of Recent Climate Change
Global Warming is now undeniable from observations in global average air and ocean temperatures, melting of snow and ice and rising sea levels.
- Eleven of the last 12 years (1995-2006) rank the warmest years since 1850. Urban heat island effects are real but local, and do not have value in the warming growth rate.
- New analyses of balloon-borne and satellite measurements show warming rates similar to surface temperature records and are constant.
- The average atmospheric water vapour content has increased since the 1980's due to the extra water vapour warmer air can hold.
- Average global ocean temperatures have increased in depths of 3000m, and the ocean has been absorbing more heat which causing seawater to expand therefore increasing sea levels.
- Mountain glaciers and snow cover has decreased in both Hemispheres which has contributed to sea levels rising.
- Ice sheets mass have been reduced, thinned or lossed.
- Sea level have rose at a rate of 1.8mm per year which is still increasing.
Continental, regional, and ocean basin scales changes in climate have been observed. These changes include Arctic temperatures, precipitation, ocean salinity, wind patterns, and extreme weather including droughts, heavy precipitation, heat waves and intensity of tropical cyclones.
- Average Arctic temperatures have increased at almost twice the global rate in the past 100 years.
- Arctic sea ice extent has shrunk by 2.7% per decade.
- Maximum area of permafrost has decreased by 7% in the Northern Hemisphere since 1900.
- Trends from 1900-2005 have been observed about precipitation and has showed huge changes throughout the globe.
- Changes in precipitation and evaporation over the ocean has increased salinity in low latitude areas.
- Westerly winds have strenghtened in both hemispheres since the 1960's.
- More intense and longer droughts over wider areas since the 1970's.
- Frequency of heavy precipitation has increased over land masses.
- Widespread changes in extreme temperatures have been observed over the last 50 years.
- There is evidence of increased tropical cyclone activity since about 1970, related to increased sea levels. The storms have become more intense and frequent.
Understanding and Attributing Climate Change
Most observations of global average temperatures since the mid-twentieth century has changed from likely to very likely due to anthropogenic greenhouse gas concentrations.
- It is likely that increases in greenhouse gas concentrations alone would have caused more warming than observed.
- It is extremely likely that climate change of the past 50 years can be explained with internal forces, and very likely not due to known natural causes.
- Warming has been detected in changes of surface and atmospheric temperatures, upper several hundred metres of the ocean, and contributing to sea level rise. The warming and cooling is very likely due to greenhouse gas increases and ozone depletion.
- It is likely there has been anthropogenic warming in the past 50 years over every continent except Antarctica.
- Small-scale temperature changes are very difficult to detect.
- Anthropogenic forces are likely contributing to changing wind patterns, causing severe storms.
- It is more likely than not that anthropogenic forces have increased occurance of heat waves.
Analysis of climate models have constraints from observations are likely to range.
- The global average warming range is from 2-4.5 oc.
- It is very likely that climate changes of seven countries prior to 1950 are from natural forces.
Projections of Future Changes in Climate
For the next two decades a warming of about 0.2 oc per decade is expected, if levels of warming were kept constant, there would still be a further warming of about 0.1 oc per decade.
Continued release of greenhouse gas emissions at or above the current rate would cause further warming very likely larger than that of the 20th century.
- Current advances in climate change models enable best estimates.
- Best estimates for climate predictions are currently at 1.1 oc-2.9 oc for low scenarios and 2.4 oc- 6.4 oc for higher scenarios.
- Warming reduces land and ocean uptake of carbon dioxide.
- Increasing atmospheric carbon dioxide concentrations lead to an increasing acidification of the ocean.
Now, there is higher confidence in projected patterns of warming.
- Warming is expected to be greatest over land and at most in the Northern hemisphere.
- Increase thawing of permafrost is expected.
- Sea ice is expected to shrink in the Arctic and Antarctic.
- Tropical storm tracks are expected to move poleward.
Anthropogenic warming and sea level rise will continue even if greenhouse gas concentrations were stabilized.
- Climate carbon cycle coupling is expected to add carbon but the magnitude is uncertain.
- If radiative forcing were stabilized by 2100 there is a 0.5 oc warming still expected.
- Thinning of the Greenland ice sheet is expected to continue beyond 2100.
- Antarctic ice sheet is projected to be too cold for melting, it is expected that the ice mass will increase due to an increase in snowfall.
- Past and future anthropogenic carbon dioxide emissions will continue to contribute to warming for more than a millenium.
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