Last October, the Intergovernmental Panel on Climate Change (IPCC) finalized its special report “Global Warming of 1.5 °C”, in response to the signing of the “Paris Agreement” in 2015, where the global mutual aim to limit global temperature increase to 1.5 °C was agreed upon.
The IPCC report outlines the impacts of global warming of 1.5 °C above pre-industrial levels. Now what would a 1.5 °C global temperature increase imply for South Asia?
The river basins of the Indus, Ganges and Brahmaputra in South Asia are seen as climate change hotspots. These river basins, which are largely fed by mountain water are home to a population around 900 million people, which is likely to increase to around 1.2 billion by 2050. Climate change is expected to hit hard in this region which is already facing natural disasters like floods, droughts, landslides and heat waves. Rainfall patterns are changing and shifts in glacier and snow melt are already having an impact on water resources required for agricultural production and the generation of energy. Further changes in the climate will likely aggravate natural hazards and threaten food security, energy production, human health, and the environment. The impacts of climate change can be especially difficult to cope with for vulnerable populations, many of whom are dependent on subsistent farming, as is the case in South Asia.
Together with an international team of researchers of the HI-AWARE consortium, I tried to find answers to this question by analyzing climate model data for changes in a range of climate change indicators over the Indus, Ganges, and Brahmaputra basins. For example, we looked at changes in rainfall patterns over the seasons, but also at changes in extreme rainfall events, which are a key driver of floods and landslides. Similarly we examined future changes in drought and heat extremes.
One of our findings is that a global temperature increase of 1.5 degrees would imply a regional temperature increase of more than 2 degrees. The culprit here is the fact that mountainous areas tend to warm up much faster than low-lying lands, a process also referred to as “elevation-dependent warming”. With the Hindu Kush, Karakoram and Himalayan mountain ranges as the basins’ headwaters, this phenomenon is particularly intense for South Asia. We also showed that 1 degree of global temperature increase with respect to preindustrial levels has already been realized to date.
Our analysis of climate change indicators shows that the impacts of a continuation of the global warming to the 1.5 degrees level are significant. For example, monsoon precipitation increases by 3 to 11% and the intensity of extreme rainfall events increases by 7-11%. Our earlier research in HI-AWARE showed that increases in extreme rainfall in the high mountain ranges would lead to severe increases in the flood frequency. Another finding is that the number of nights with very high nighttime temperature, hampering sufficient cooling of the human body, would increase by around 10% on average.
We compared climate change impacts at 1.5 and 2 degrees global warming scenarios and found that changes in the analyzed climate change indicators in general increase linearly with temperature increase. Because the global 1.5 degrees target is extremely ambitious we also looked at scenarios of higher global warming, which may be more likely if the current pace of warming continues. These scenarios would lead to a regional warming of 3.4 to 5.8 °C at the end of the 21st century compared to preindustrial levels. With that other adverse effects of climate change would be worse. For example, the intensity of extreme rainfall events could increase by up to 50%.
Last year I contributed to research led by Utrecht University showing that Asia’s glaciers would lose around one third of their present-day ice mass by the end of the century under a 1.5 degrees scenario. This loss could be up to two-thirds at higher global warming scenarios. These changes will likely lead to strong shifts in timing of water supply from the high mountains, being an important factor to include in water availability scenarios for South Asia.
Although I am convinced that climate change mitigation efforts will strongly intensify in the coming years, I am skeptical that the global mitigation targets set out in the Paris Agreement will be met. Therefore, I am firmly convinced that the full range of climate projections needs to be taken into account to formulate robust climate adaptation policies, and should not be limited to global warming scenarios of 1.5 or 2 degrees. Preparing for 1.5 or even 2 degrees of global warming will probably not be enough.