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Sulphur dioxide (SO2) is a hazardous air pollutant, which is mostly emitted from burning of fossil fuels, and has an adverse impact on the human health and ecosystem functioning. The COVID-19 natural anthropause (lockdown) provides a great opportunity to understand the changes in SO2 pollution across the globe, as there was a temporary standstill for most human activities. Therefore, we analyse the changes in global SO₂ pollution during lockdown compared to pre-lockdown and identify its hotspots driven by human activities using satellite measurements, reanalysis data and emission inventory. We observe a decline in SO₂ pollution of about 2.21 % in its global average, −21.05 % in Indo-Gangatic Plain, −16 % in East China, −7.67 % in East United States of America, −3.99 % in Western Europe and −3.85 % in Middle East owing to the halt in human activities such as industrial and transport operations, as found from the emissions inventory. There are point and aerial hotspots of SO₂ pollution across the globe (e.g. cities or industrial units), which also show a decrease (20–30 %) in SO₂ pollution during the anthropause. Fossil fuel burning in thermal power plants is a major source of SO2 pollution, and it has declined notably (1–12 %) during the lockdown in the major coal consuming countries such as the United States, China, Japan, Canada, Brazil, Australia, France, Germany, Spain, Italy and the United Kingdom. Therefore, lockdown provides a clear understanding of global human-driven hotspots of SO₂ pollution and their changes, which would help us to make better and effective air pollution mitigation strategies.

We present a detailed long-term (1997–2019) analysis of observed cyclone-induced surface cooling (or cold wake) in the Arabian Sea. Here, the analysis is performed for 33 cyclones that drove significant cooling at the sea surface in three different seasons: the pre-monsoon, monsoon and post-monsoon. Our study shows that cyclones can cool the sea surface up to 4.76° C after their passage, depending on the intensity, duration and other factors that contribute to cooling. The monsoon and pre-monsoon cyclones show stronger cooling, but the post-monsoon cyclones exhibit a longer duration (8–10 days) of cooling and slower recovery time (15 days). In general, the pre- and monsoon cyclones exhibit a strong positive correlation with the Latent Heat Flux, whereas the post-monsoon cyclones show a higher correlation with Ekman Pumping Velocity, wind stress and intensity of cyclones. The cold wake composite analysis for the El-Niño, La-Niña and Normal years shows that cyclone-induced cooling is similar in El-Niño and La-Niña years, and the cooling is more dominant during the negative Indian Ocean Dipole (IOD) than that in the positive IOD years. Co-occurrence of positive IOD and La Niña events has led to more intense cyclones in recent decades. The power dissipation index, accumulated cyclone energy and oceanic heat content also show an increasing trend in AS and favour rapid intensification of cyclones. Since the drop in SST normally impedes cyclones from intensification, our study is important and the findings of this study will aid in tropical cyclone predictions. In response to rapid warming of Indian Ocean in recent decades, extreme events such as cyclones are expected to increase in the context of climate change. [ABSTRACT FROM AUTHOR]

Anthropogenic emissions have produced significant amount of carbon dioxide (CO2) in the atmosphere since the beginning of the industrial revolution. High levels of atmospheric CO2 increases global temperature as CO2 absorbs outgoing longwave radiation and re-emits. Though a well-mixed greenhouse gas, CO2 concentration is not uniform in the atmosphere across different altitudes and latitudes. Here, we uncover a region of high CO2 concentration (i.e. CO2 pool) in the middle troposphere (500–300 hPa) over the Indo-Pacific Warm Pool (IPWP, 40° E–140° W, 25° S–25° N), in which the CO2 concentration is higher than that of other regions in the same latitude band (20° N–20° S), by using CO2 satellite measurements for the period 2002–2017. This CO2 pool extends from the western Pacific to the eastern Indian Ocean. Much of the CO2 pool is over the western Pacific Ocean (74.87%), and the remaining lies over the eastern Indian Ocean (25.13%). The rising branch of Walker circulation acts as a "CO2 Chimney" that constantly transports CO2 released from the natural, human-induced and ocean outgassing processes to the middle and upper troposphere. The CO2 pool evolves throughout the year with an average annual trend of about 2.17 ppm yr−1, as estimated for the period 2003–2016. Our analysis further reveals that La Niña (El Niño) events strengthen (weaken) the CO2 pool in the mid-troposphere. The radiative forcing for the CO2 pool suggests more warming in the region and is a grave concern for global warming and climate change. [ABSTRACT FROM AUTHOR]