WP1: Radiative effects of clouds, water vapour and carbon dioxide on monsoons
Clouds, water vapour (WV) and carbon dioxide are abundant in the atmosphere above monsoon regions. However, the influences of these processes – and in particular their radiative effects – on monsoon circulations have not been systematically investigated. In WP1, we used a novel suite of idealised climate-model simulations to quantify the individual roles of clouds, WV and carbon dioxide in controlling both the present-day monsoon and changes in the monsoon in response to an increase in carbon dioxide concentration. For the present-day monsoon, we found that seasonal north/south migrations of clouds and WV are fundamental for shaping the monsoon; in the absence of these seasonal feedbacks, monsoon rainfall would be substantially stronger and the timing of monsoon onset would shift by several weeks. Under an abrupt increase in carbon dioxide concentration, changes in clouds exert a strong control on the monsoon response. Changes in WV and carbon dioxide also influence the monsoon response, and their effects are comparable both in magnitude and spatial structure. These results have been published in Byrne & Zanna (2020) and featured in a review article on monsoons & climate change written on behalf of the UN’s World Meteorological Organisation and co-authored by the researcher (Wang, Biasutti, Byrne et al., 2021).
Following on from the work described above, we are also using observational datasets to quantify the coupling between clouds, circulation and top-of-atmosphere energy fluxes both in monsoon regions and across the tropics. We have found that the atmospheric circulation is playing a central role in controlling clouds and their radiative effects on both year-to-year and decadal timescales. This is an important new insight into how tropical clouds affect Earth’s energy balance, with important implications for estimating how climate will change over the coming decades. This work is expected to be submitted for publication in early 2023.
WP2: Influence of the ocean on extreme temperatures in monsoon regions and across tropical continents
Extreme temperatures are becoming more frequent and more intense as climate warms, affecting humans and ecosystems around the world. However, despite this societal importance, the physical drivers of extreme temperatures in a changing climate are not well understood, particularly in tropical regions. In WP2, we investigated the hypothesis that – because of active convection and weak Coriolis forces in the tropical atmosphere – ocean temperatures impose a strong constraint on extreme temperatures over tropical continents. We developed this hypothesis into a novel quantitative theory for the tropical land temperature distribution in a changing climate. This theory – now known as the ‘drier get hotter’ theory – links extreme temperatures over monsoonal regions and tropical land to the surface temperature of neighbouring oceans and to the dryness of the land surface. The theory has been verified using state-of-the-art climate simulations, demonstrating – for the first time – that tropical heatwaves are tightly controlled by the oceans. This work was recently published (Byrne, Nature Geoscience, 2021) and has established a new framework of understanding for extreme temperatures that is expected to shape the next decade of tropical heatwave research.
Overview of the dissemination and exploitation of the project results:
The project results have been widely disseminated to the international climate-science community, including 6 conference talks, 6 workshop talks and 11 invited seminars over the course of the fellowship. Project results have also been disseminated through four scientific publications in leading journals, with a further publication expected in 2023. In addition, a variety of activities have been undertaken during the project to communicate with broader society, including:
• Article aimed at a broad audience in Horizon (the EU research magazine) showcasing the project research.
• Talks communicating the latest climate science for the general public, including at the Royal Society of Edinburgh in 2021.
• The researcher has an established following on Twitter (~1,700 followers) and uses this platform to communicate project activities. For example, a tweet highlighting the Byrne (Nature Geoscience, 2021) study generated more than 2,000 engagements.
