Weeks of flooding in Bangladesh in August 2017 reportedly claimed the lives of over 100 people, displaced tens of thousands more, and destroyed more than one million acres of crops.
The flooding was centered around the Brahmaputra River, one of Asia’s major rivers, which flows from China through northeast India before reaching Bangladesh. Researchers at the Bangladesh University of Engineering and Technology recently looked at how the river’s annual flood cycles will be impacted by global warming and determined that the more the world warms, the more common and severe Brahmaputra floods will become.
If global temperatures rise 2 degrees Celsius, they write in a study summarizing their findings published in the journal Climatic Change last September, “Results indicate that floods will be more frequent and flood magnitudes greater” than they would be at just 1.5 degrees Celsius of warming.
The study was carried out as part of the HELIX project, which involves more than 50 scientists from 16 institutions in 13 countries who have spent the past four years examining the potential impacts of global temperatures rising an average of 1.5°C, 2°C, 4°C, and 6°C compared to pre-industrial levels.
According to HELIX researchers, global temperatures have already risen about 1°C, and at least another 0.5°C of warming is likely given the amount of greenhouse gases we’ve already pumped into Earth’s atmosphere. But we have yet to experience the full impacts of that warming, given that ice sheets and oceans will take decades to respond to rising temperatures.
By signing the Paris Climate Agreement, the world’s nations committed to keeping global temperature rise in the 21st century “well below 2 degrees Celsius” and, if possible, to limit the temperature increase to 1.5°C.
Meeting those targets will require a rapid drawdown of greenhouse gas emissions. But even if we do manage to rapidly decarbonize the global economy, some impacts of climate change are probably still unavoidable, according to HELIX project leader and University of Exeter professor Richard Betts.
Some impacts “already locked in”
If we were to halt global warming “well below” 2°C, for instance, HELIX research suggests that flooding risks would indeed be abated — but that risk still doubles at 1.5°C of warming (it increases by 170 percent at 2°C). Also, sea levels would still rise by a half meter by the end of the century, which would have the biggest impact on small island states and low-lying countries — like Bangladesh, where HELIX researchers estimated 2.5 million people would be affected.
“Regarding the impacts that are already locked in, I think the most important finding is the potential impact of increases in both coastal and river flooding, especially in south and east Asia,” Betts told Mongabay.
“A sea level rise of up to 0.5 meters by 2100 may already be unavoidable even in a scenario of deep emissions cuts — we estimate that this could inundate 2000 square kilometers in Bangladesh, which is 1.6 percent of the country and would affect 2.5 million people. Even if global warming is limited to 1.5 degrees Celcius, we estimate that the associated increased rainfall would cause river flooding affecting one to two million people in Bangladesh, over five million in India, and over 10 million in China.”
Betts added that all of these figures are for current levels of defences against flooding in those Asian countries, “underlining the need to consider improving such defences as an adaptation to climate change.”
Aggressive action to rein in global warming could still prevent its worst impacts, Betts notes. If emissions were to continue unabated and global temperature increases exceed 4°C, increased rainfall would further enhance the risk of floods by raising river levels, which, combined with sea level rise, could impact as many as 12 million people in Bangladesh, especially if a storm surge from a tropical cyclone compounded these effects.
Of course, the impacts would not be limited to South Asia. At 4°C of warming, most countries would see increased flood risks. The HELIX researchers found that countries representing 73 percent of the world’s population and 79 percent of global GDP would experience a five-fold increase in the risk of river floods and flood damage.
“A warmer atmosphere can hold more water, so rainfall would be more intense,” Betts said in a statement. “This would inevitably mean more flooding, and our research suggests the largest increase in flood risk would be in parts of America, Asia and Europe.”
Climate adaptation necessary
While a wetter global climate would lead to less drought in some parts of the world, droughts would become more common in other regions, such as parts of Africa and southern Europe. And all of these impacts of global warming would impact agricultural production, as well.
“Some places will do better and some will do worse,” Betts said. “For example, with warming of 4°C, some parts of Europe would have improved production of certain crops, while other crops would be harder to grow. In Britain, it would become harder to grow wheat but easier to grow maize.”
On the whole, Betts noted, food security would be at risk around the world, not just due to changing crop yields but also because of extreme weather events.
“It is clear that humanity has a huge challenge to deal with here,” Betts said. “The countries of the world have agreed to try to minimise global warming, and the debate has now moved on to exactly how to achieve this — but we will have to live with some changes that are already unavoidable.”
That means that the chief takeaway of HELIX’s research for policymakers is that, while the greatest risks from climate change can still be avoided by reducing global emissions, it’s too late, at this point, to avoid all impacts. Efforts to adapt to the new global climate will therefore be required.
But it’s also important that policymakers around the world understand that, even if we were to make deep and rapid emissions cuts, we would not see the difference those cuts made immediately.
“With some level of warming and sea level rise already in the pipeline no matter what we do, we won’t see a reduction in impacts or even a sudden levelling-off — impacts are projected to increase at the same rate in all scenarios for the next couple of decades or so, and after that they merely increase more slowly in the deep emissions cuts scenarios,” Betts told Mongabay.
“However, they continue to increase more rapidly in the high emissions scenario. So the point is, while we can make a difference to the longer-term outcomes in the second half of this century through reducing emissions, we can’t affect the near-term changes which are already locked in, so we need to adapt.”
• Mohammed, K., Islam, A. S., Islam, G. T., Alfieri, L., Bala, S. K., & Khan, M. J. U. (2017). Extreme flows and water availability of the Brahmaputra River under 1.5 and 2° C global warming scenarios. Climatic Change, 145(1-2), 159-175. doi:10.1007/s10584-017-2073-2