The IPCC has blamed man-made emissions for warming of the globe and long term climate change. Limiting climate change, therefore, will require substantial and sustained reduction of greenhouse gas emissions. This is the message to politicians and policy makers of the world, says Dinesh C Sharma.
The four-month summer monsoon season has officially ended on September 30. Nearly 40 percent of the Indian landmass has received excess rainfall, with flooding being reported from many parts in western India. The monsoon advanced rapidly soon after its onset in the first week of June, and caused havoc in the Himalayas and resulted in the Kedarnath tragedy. At the same time, some areas in the eastern parts of the country have received deficit rainfall. If its advance was rapid, monsoon’s retreat has been slower.
Is this behaviour of the Indian monsoon normal or it is part of larger climatic change? While the Indian Meteorological Department may not have an answer to this, the latest report of the Nobel prize-winning Intergovernmental Panel on Climate Change headed by Indian climate scientist Dr Rajendra Kumar Pachauri, does offer some clues.
The report -- full draft of which was made public on Monday following release of a summary last week -- elaborates on the impact of global warming on the monsoon. Going by the findings of this report, one can say that the behaviour of the monsoon being witnessed now is a clear indicator of the future.
“It is likely that the area covered by monsoon systems will increase over the 21st century. While monsoon winds are likely to weaken, monsoon precipitation is likely to intensify due to the increase in atmospheric moisture. Monsoon onset dates are likely to advance or not to change much. Monsoon retreat dates will likely be delayed, resulting in lengthening of the monsoon season in many regions,” the report has concluded.
This conclusion is based on a number of studies on Indian monsoon which have reported variability in decade-to-decade rainfall data. There are regional inconsistencies -- rainfall has decreased over central India along the monsoon trough due to a number of factors including black carbon, sulphate aerosols, land-use changes and SST (sea surface temperature) rise over the Indo-Pacific warm pool.
“The increase in the number of monsoon break days over India, and the decline in the number of monsoon depressions are consistent with the overall decrease in seasonal mean rainfall. The frequency of heavy precipitation events is increasing, while light rain events are decreasing,” the report has noted.
The strength and timing of monsoon -- which affects all tropical continents (Asia, Australia, the Americas, and Africa) is related to moisture content in the atmosphere, contrast in land-sea temperatures, presence of aerosols in the atmosphere and other factors. Overall, the report says, monsoonal rainfall is projected to become more intense in future and will affect larger areas because atmospheric moisture content increases with temperature. However, localised effects of climate change on regional monsoon strength and variability remain “complex and more uncertain”.
The likely impact on monsoon is just one of the fallouts of global warming. There will be similar changes across the globe -- higher temperatures, more of extreme weather events such as heat waves and heavy rainfall, rise in sea levels, melting of glaciers and so on.
While all these impacts of global warming have been known for many years, what’s new in the report is the clarity with which it has pinpointed the reasons behind it. In no uncertain terms, the scientific panel has provided evidence that global warming is real and that it is largely man-made.
The warming of the climate system is “unequivocal”, the report has concluded, and since the 1950s, it says, many of the observed changes are unprecedented. In the past hundred years, the atmosphere and oceans have warmed, snow and ice covers have diminished, sea level has risen and the concentration of greenhouse gases has increased. This trend is likely to continue over this century if no urgent measures are taken. Some of the changes are irreversible.
Each of the last three decades has been successively warmer at the earth’s surface than any preceding decade since 1850. In the northern hemisphere, 1983-2012 period was likely the warmest 30-year period of the last 1,400 years. The overall warming in the period 1880-2012 is pegged at 0.85 degree.
The main contention of climate deniers -- with reported financial links to fossil fuel industry -- is that the observed changes are due to natural factors and not due to man-made factors. In other words, fossil fuel burning and other sources of emissions are not to be blamed. The IPCC panel -- based on evidence from scores of studies -- says it has indeed detected “human influence” in warming of the atmosphere and the oceans and other manifestations of it. With 95 to 100 percent probability the panel says that human influence has been “dominant cause” of observed warming since the mid-20th century.
The proof of human influence comes from data on carbon dioxide, methane, and nitrous oxide concentrations in the atmosphere, which have shot up greatly. Carbon dioxide concentrations are up by 40 percent since pre-industrial times, primarily due to fossil fuel emissions and emissions caused due to deforestation. Based on concentration of these gases in ancient ice cores, scientists have concluded that the rate of increase of these gases during the past century has been unprecedented in the last 22,000 years.
The process of compiling and preparing assessment reports has been made robust to avoid bloopers like the one reported about melting of Himalayan glaciers in the last synthesis report in 2007. Every word of the present report has been verified and all projections are couched in carefully chosen and defined phrases like “likely” and “virtually certain”.
The report acknowledges the so-called pause in global warming -- touted by deniers to debunk the science behind it -- observed during 1998-2012 period when the warming rate was 0.05 degree per decade. This is much smaller rise than the rate calculated since 1951.
The trend (of slower warming), the report says, is “due to natural variability” and because “trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends.” The beginning of this period -- 1998 -- was a strong El Nino year and the period saw eruption of medium-sized volcanoes that cooled the climate a bit.
Since the so-called pause in warming has been a major bone of contention between scientists and deniers as well as within scientific community, it would have been better if IPCC had elaborated further on this issue. Climate skeptics claim that the 15-year hiatus in warming continues beyond 2012 and that climate change is not going to be such a crisis for a few more decades.
If global warming is here and now, what about the future trends and its likely impact? Continued emissions of greenhouse gases, the report warns, will cause further warming and changes in all components of the climate system.
In the medium term -- between 2016 and 2035 -- the global mean surface temperature rise will be in the range of 0.3 degree C to 0.7 degree C relative to 1986-2005 period. It is “virtually certain” that there will be more frequent hot and fewer cold temperature extremes over most land areas on daily and seasonal timescales as global mean temperatures increase. It is very likely that heat waves will occur with a higher frequency and duration. Occasional cold winter extremes will continue to occur.
The IPCC has blamed man-made emissions for warming of the globe and long term climate change. Limiting climate change, therefore, will require substantial and sustained reduction of greenhouse gas emissions. This is the message to politicians and policy makers of the world. The problem has been identified. Now politicians will have to find solutions. The first opportunity to move towards possible solutions will present itself in November when the world gathers in Warsaw for the next round of climate change negotiations.
Dinesh C Sharma is a science journalist and author based in New Delhi.