NEW DELHI: Climate scientists are more certain that ever before that global warming is being caused by human activities, particularly the burning of fossil fuels. A leaked draft of the first of three reports comprising the Intergovernmental Panel on Climate Change's Fifth Assessment Report states that it is "at least 95% likely" that human activities are the main cause of climate change since the 1950s.
The Intergovernmental Panel on Climate Change, established by the United Nations and World Meteorological Organisation, is tasked with providing scientific guidance to governments across the world in developing policies to counter climate change. The IPCC is not a research organisation. Under the aegis of IPCC, scientists, researchers, think tanks, and not for profit organisations assess and process the work in the field of science relating to climate change.
Scientific certainty over the human contribution has become more robust over the last 25 years. In the last assessment report of the IPCC released in 2007, scientists were able to establish a 90% certainity, in 2001 it was 66% and in 1995 it was 50%. Calling into question the position taken by a minority of scientists that the global warming experience over the last half century was a natural climate phenomena.
The draft report, seen by ET, due to be released at the end of September, finds that greenhouses gases like carbon dioxide have contributed to a global mean surface warming in the range of 0.5 degrees Celsius to 1.3 degrees Celsius between 1951 and 2010. Accounting for the cooling effects of aerosols (-0.6degree to 0.1 degree), and variations due to natural climate processes (-0.1 degree to 0.1 degree), the draft report finds a warming of 0.6 degrees over the period.
Climate scientists say it is "extremely likely" that human influence on climate caused more than half of the increase in global average temperature. The concentrations of greenhouse gases — carbon dioxide, methane and nitrous oxide have all increased since 1750. The concentration of carbon dioxide is up by 40% from the pre-industrial levels. The report states a 20% rise in the levels of carbon dioxide since 1958, when systematic atmospheric measurements began. The levels of methane and nitrous oxide in the atmosphere have exceeded pre-industrial levels by 150% and 20%, respectively.
The draft report takes cognisance of the fact though global temperatures have been rising that the rate of warming over the past 15 years (1998 to 2012) is smaller than the trend since 1951. The draft IPCC report states that the slowdown in the warming rate could be on account of natural variations in weather, and other factors like greater than expected quantities of volcanic ash, a decline in heat from the sun during a current 11-year solar cycle, more heat being absorbed by oceans.
But a slower warming rate provides no consolation, nor should it be a pretext to slowdown efforts to counter climate change. The World Metereological Organisation has reported that the decade from 2001-2010 was the warmest since the start of modern temperature measurements in 1850. The IPCC draft report states that the global mean temperature change between 2016 and 2035 will be in the range of 0.3 degrees to 0.7 degrees Celsius.
The IPCC report stresses that long-lived greenhouses gases like carbon dioxide will determine the nature of global warming. The report warns that continued greenhouse gas emissions would cause further warming. Emissions at current levels or higher would lead to changes in all components of the climatic system. The draft report is "virtually certain" than in most places, there will more hot and fewer cold temperature extremes and that it is "very likely" that heat waves will occur with higher frequency and duration. The draft report states that scientists are highly confident that the warming will be larger over oceans and that Artic region will warm most rapidly.
