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Carbon neutrality likely to increase extreme weather events: Study

Research highlights greenhouse gas emissions need to reach their highest point by 2025 & decrease by 43% this century. Extreme weather

By Wahid Bhat
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As per the current climate models, if we continue on our current trajectory of greenhouse gas emissions, the planet could warm by as much as 4.3°C by 2100. This is a worst-case scenario if we don’t take adequate measures.

The Paris Climate Agreement, which has been signed by 195 countries, aims to limit this increase to 2°C, and ideally to 1.5°C, above pre-industrial levels by the end of the century. However, the Intergovernmental Panel on Climate Change has reported that we’ve already seen a 1.1°C increase up until 2020.

The new research published in Nature Communications also highlights that in order to achieve the 1.5°C target, greenhouse gas emissions need to reach their highest point by 2025 and then decrease by 43% for the remainder of the century.

Extreme Weather on the Rise

While the primary focus is on implementing strategies to counter greenhouse gas emissions and achieve carbon neutrality by 2025, a new study published in Nature Communications has highlighted the urgent issue of atmospheric aerosols and their counterproductive effect on climate warming.

In addition, research conducted by Associate Professor Pinya Wang from Nanjing University of Information Science & Technology, China, and his team, has underscored the increasing frequency and intensity of extreme weather events, from floods to heatwaves, and their potential global impact. This is based on a projected increase in global surface air temperature and annual mean precipitation of 0.92°C and 0.10mm per day by 2100, respectively.

The research team used the Community Earth System Model to determine that a decrease in atmospheric aerosols could have a negative impact on the global climate, exacerbating the occurrence of extreme weather events more than changes in greenhouse gases or the tropospheric ozone layer (up to 10km above ground level).

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However, these three factors are closely interconnected. Wang and his team noted that reducing greenhouse gas emissions, particularly those resulting from the processing and burning of fossil fuels, also reduces the formation of other pollutants, such as tropospheric ozone and aerosols.

Ozone and aerosol climate effects

This ozone is formed through chemical reactions of emissions from vehicles and smokestacks, often manifesting as smog in cities. Dammam in Saudi Arabia has recently been identified as having the most problematic atmospheric particulate pollution.

China, a country often associated with smog, would need to reduce vehicle and smokestack emissions of sulfur dioxide, nitrogen oxides, primary particulates <2.5μm diameter, and volatile organic compounds by a significant 93%, 93%, 90%, and 61% respectively, to achieve carbon neutrality by 2060, according to recent studies.

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Tropospheric ozone contributes to the planet’s temperature by increasing radiative forcing, which traps more incoming solar radiation. On the other hand, aerosol particulates can have contrasting effects, with sulfates causing cooling and black carbon causing warming.

The scientists referenced recent studies that examined the impact of the coronavirus pandemic on extreme weather, finding that reduced aerosol emissions in 2020 led to increased air temperature and decreased humidity, resulting in a higher incidence of wildfires in the United States.

The research team used models to examine the forcing from greenhouse gases, ozone, and aerosols under a carbon neutrality scenario known as Shared Socioeconomic Pathway 1–1.9.

Future climate scenarios modeled

In this scenario, carbon dioxide concentrations peak at 437ppm by 2050 and decline to 400ppm by 2100, while methane reduces from the current 1,884ppb to 1,061ppb by the end of the century. During the same period, sulfur dioxide emissions would also decline from the current 3gm−2a−1 to 1gm−2a−1, black carbon from 1gm−2a−1 to 0.1gm−2a−1, and organic carbon from 0.2gm−2a−1 to 0.14gm−2a−1.

Compared to a 2020 baseline, the researchers found that by 2050, the planet’s overall surface air temperature would increase as radiative forcing increases, peaking at 0.2°C over Greenland, based solely on greenhouse gas emissions.

However, when aerosols were included in the models, surface air temperatures across the Earth rose significantly, reaching a maximum of 2°C throughout the mid-high Northern Hemisphere latitudes. This could be slightly offset by a decrease resulting from the effect of tropospheric ozone. By 2100, the warming caused by aerosol reduction continues to increase surface temperature.

The model also identified changes in annual mean precipitation across the planet under the same forcings. It found that tropical oceans, especially the Western Pacific, experienced increased rainfall under greenhouse gas-only forcing.

Adding a reduction in aerosols to the simulation forcing exacerbated rainfall throughout the Northern Hemisphere, but had an opposing effect across the Southern Hemisphere, while reduced tropospheric ozone had little impact.

Specific humidity on the Rise

Regions such as South, East, and Southeast Asia are projected to experience the greatest increase in precipitation, reaching 0.3mm per day. This pattern remains the same throughout the rest of the century, but with a larger amplitude, resulting from increased atmospheric water vapor due to warmer temperatures enhancing evaporation and therefore specific humidity.

The researchers used these extreme temperature and precipitation models to simulate the frequency and magnitude of heat waves. Under greenhouse gas-only forcing, heat waves were projected to occur five days per year, each event lasting four days with a temperature increase of 0.25°C per day.

However, when the decline in aerosol abundance was included in the model, a significant increase in heat wave intensity was projected. Heat waves were predicted to occur over 40 days per year, with each event lasting 20 days and a daily global temperature rise of 0.75°C per day by 2050. By the end of the century, these figures are projected to increase even further, with 50 days per year experiencing heat wave conditions, individual events lasting 28 days, and daily temperature fluctuations of 1.5°C.

This research underscores the ongoing need for more sustainable solutions to address not only greenhouse gas emissions, but also associated pollutants. This is crucial in order to give the world a better chance of reaching ambitious climate targets and mitigating the wide range of environmental, economic, and social impacts that global warming is likely to cause in the coming decades and generations.

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