Expect extreme weather to turn more calamitous

Even if all the countries decrease emissions to stick to the 2 degree-level as per the Paris Agreement, there will still be an increase in extreme weather and climate events.
Image used for representational purposes only.
Image used for representational purposes only.

Over the past month, the people in the northeastern states of Assam, Arunachal Pradesh, and Meghalaya have endured heavy monsoon rainfall and resultant landslides and flooding of multiple rivers. In Assam alone, the death toll has crossed 170, and over 3 million people in 30 districts have been affected, with many lakhs displaced from homes and staying in makeshift relief camps.

Floods preceded this in May that affected people in 27 out of 34 districts. Neighbouring Bangladesh has also been similarly affected by the floods. While flooding in these parts nearly occurs yearly, the prolonged flooding over large parts of the northeast this year has made this event unusual.

A few months back, we had another unusual event—the prolonged heat-wave-like conditions over large parts of central and northwest India and southeast Pakistan starting as early as March this year. In a recent “event attribution” study, we estimated that without the human-induced climate change, the heat wave this year would have occurred about once in 3000 years but now occurs perhaps once in 100 years—an increase in the likelihood of about 30! While a similar attribution study for the Assam floods is yet to be carried out, it is entirely consistent with the effects of climate change caused by human activity.

The Intergovernmental Panel on Climate Change (IPCC) recently released three Sixth Assessment Reports. They strongly emphasise that human emissions of greenhouse gases and other pollutants have increased global temperatures. They assess that extreme weather and climate events (such as heat waves and heavy rainfall) have become more severe, leading to increased impacts on human and natural systems across the globe.

Heat-related events have increased in frequency, intensity and duration due to human activity everywhere in the world. Increases in heavy rainfall events have been harder to track globally due to short data records.

Still, several regions have documented increased incidence of heavy rainfall events and some others of droughts. Several regions are also seeing an increase in extreme compound events where droughts and heat waves happen together, or stronger cyclones cause heavier rainfall with increased flooding due to sea level rise.

The documented increases in extreme events tell the story of the planet’s warming of about 1.2 degrees centigrade to date (relative to before the advent of industrialisation). We are by no means done with warming and resultant climate change. Our continued emissions of carbon dioxide and other greenhouse gases will further warm the planet till we stop those emissions.

If we consider all the pledges and promises made by all nations to halt net emissions, we will have warmed the planet by about 2.7 degrees centigrade. Even if all the countries of the world step up and reduce their emissions rapidly to keep global temperature change under the Paris Agreement goal of 2 degrees (or the more ambitious 1.5 degrees) centigrade, we will still see an increase in the extreme events from current levels.

We can expect the hazards of extreme weather and climate events to increase in frequency, magnitude and duration. However, we must know how much worse they can get and how to avoid the worst impacts of these events. Event attribution studies such as the one we carried out for this year’s heat wave indicate that there could be a 1-in-50 or even 1-in-5 chance of such an event occurring in any year (instead of the current 1-in-100) when global temperatures reach 2 degrees centigrade above pre-industrial levels.

But we don’t have enough such studies that give us a long-term perspective on future changes of the hazards we should care about. This is different from disaster mitigation as it is currently done, where short-term weather forecasts inform how disaster response professionals act to prevent loss of lives and property. By focusing exclusively on the here and now, we are missing a chance to look ahead and see that it will get much worse. While action plans at the national and state levels attempt to look ahead and plan for climate change, there are concerns that the focus on extreme weather and climate events may be inadequate.

I have so far just discussed the changing physical hazard. A more comprehensive look at the changing risks will involve analysing changing exposure and vulnerability of the country—the things that turn extreme weather events into a disaster. In addition to the apparent toll on human lives and livelihoods, the impact of events is felt across multiple sectors. For example, agricultural production—the estimated loss of wheat crop due to the early heat wave this year is nearly 20% in Punjab and Haryana, and standing crops lost to floods in Assam are in the tens of thousands of hectares. As we move into an era of increasing hazards, what are the added risks to food security, infrastructure and the overall economy? Few systematic studies address such questions in the Indian context, and we must address them.

Krishna AchutaRao

Professor and Head, Centre for Atmospheric Sciences, IIT Delhi


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