According to the Intergovernmental Panel on Climate Change (IPCC1), temperature has increased by about 0.74C in the last century and is expected to increase at 0.2C per decade, or 1.4 - 5.8 degrees Celsius by 2100. Warming of a few degrees is minor compared with day-to-day or seasonal variations in temperature. However, in global climate terms it is much larger than any of the climatic changes experienced during the past 10,000 years. A few degrees of global warming will lead to more heat waves and fewer frosts. More fires and droughts are expected in some regions of the world and more intense rainfall and resultant flooding in other areas.
The increase is expected to occur unevenly, with higher elevations and higher latitudes experiencing greater temperature changes than lower elevations and equatorial regions. These effects will get worse and there is a risk of reaching tipping points at which carbon release from permafrost and vegetation will accelerate global warming. The point at which this becomes very dangerous is not clear but 2°C increase is the most commonly accepted level.
The lowest scenario which IPCC looks at has CO2e stabilizing between 445 and 490 ppm and temperature between 2.0 and 2.4C. This requires an emissions peak by 2015 and a reduction by 2050 of 50% to 85% from year 2000 levels. [Non IPCC comment] This sort of global reduction implies a much greater reduction for developed countries given the equity and inevitability of developing countries closing the gap. No one country, company or technology will be sufficient to stop global warming. We need a mix of solutions to focus on using energy more efficiently and reducing its carbon intensity – it is everyone’s responsibility.
The Intergovernmental Panel on Climate Change (IPCC) concludes, "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] via the greenhouse effect.
Carbon dioxide is the main culprit
Rising temperatures therefore are due primarily to the buildup of carbon dioxide (CO2) in the atmosphere from the burning of increasing amounts of fossil fuels, with land-use change providing another significant but smaller contribution. Once released into the atmosphere, CO2 traps heat that would otherwise escape back into space. The concentration of CO2 in the atmosphere has risen by 30% to almost 380ppm since the start of the Industrial Revolution in 1760.
An increase in methane is also worrying
It is very likely that the observed increase in methane concentration is predominantly due to agriculture and fossil fuel use. Methane growth rates have declined since the early 1990s, consistent with total emission (sum of anthropogenic and natural sources) being nearly constant during this period. The increase in N2O concentration is primarily due to agriculture. These increases have enhanced greenhouse effect, which has contributing to a warming of the Earth's surface by 0.74°C over the last hundred years.
How much hotter is our planet getting?
Temperature records go back to the late 19th Century and show that the global average temperature increased by about 0.74C in the 20th Century.
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