A research study, titled ‘Human-driven greenhouse gas and aerosol emissions cause distinct regional impacts on extreme fire weather’, conducted by University of California, Santa Barbara, United States, was published in the journal Nature Communications in January 2021.
The study examined the weather under various combinations of human influences since 1920, isolating individual effects and their impacts on extreme fire weather risk. Extreme fire weather behaviour is characterised by its high rate of spread and presence of fire whirls. For example, forest fire or bush fire immediately becomes erratic and goes beyond direct control.
Several past studies have observed that human activities and their products like greenhouse gas emissions, and air pollution have had the potential to raise the risk of wildfire outbreaks. However, their specific influence had not been studied so far. According to this new study, greenhouse gases (GHGs) emissions and air pollution, caused by human activities, had distinct regional impacts on extreme outbreaks of wildfire.
The following are the highlights of the study:
- Heat-trapping GHG emissions were the dominant contributors to increases in temperatures worldwide.
- Biomass burning increases greenhouse gas-driven warming and affects different regions.
- GHG emissions had raised the risk of extreme fire weather by 20 per cent from pre-industrial levels in western and eastern North America, the Mediterranean region, Southeast Asia, and the Amazon region by 2005.
- By 2080, GHG emissions are expected to increase the risk of extreme fire weather by at least 50 per cent in western North America, equatorial Africa, Southeast Asia, and Australia.
- The increase in the risk of extreme fire weather would be twice in certain regions including the Mediterranean region, southern Africa, eastern North America, and the Amazon region, in this period.
- Surge in GHG emissions dropped the relative humidity and escalated the surface wind over the Amazon. This added to warmer temperatures and the growing risk of wildfires.
- There was a 30 per cent increase of extreme fire weather risk over the Amazon and western North America during the 20th century caused by biomass burning.
- The risk of extreme fire weather in western Australia and the Amazon is also amplified because of changes in land use pattern.
- Industrial aerosols blocked some of the solar radiation from reaching the ground and helped cooling the climate. But aerosols blocking provided little or no relief for extreme fire-weather risk in the 20th century as they were reduced over most regions.
- These reductions drove warming and drying conditions over eastern North America and Europe. The increase in dryer conditions lead to extreme fire-weather risk. The scientists predicted that there is something that is compensating greenhouse gas warming, and balancing the temperature. They did not have a clue on the details of how the compensation will continue in the future.
- In Southeast Asia, where aerosols emissions are expected to continue, there may be a weakening of the annual monsoon leading to drier conditions, and an increase in extreme fire weather risk. Southeast Asia relies on the monsoon, but aerosols cause so much cooling on land that it actually can suppress a monsoon.
It is expected that the study at a regional scale would help understand the fire risk and will be useful in mitigation and planning purposes. The study will aid in making climate policy by revealing how human actions would affect the climate in future.
Greenhouse Gases
Greenhouse gases (GHGs), are compound gases that trap heat or longwave radiation in the atmosphere. Their presence in the atmosphere makes the Earth’s surface warmer. Sunlight or shortwave radiation easily passes through these gases and the atmosphere. This radiation is absorbed by the surface of the Earth and is released as heat or longwave radiation. The molecular structure of GHGs allows them to absorb the heat released or trap them in the atmosphere and re-emit them back to the earth. This heat-trapping phenomenon is known as the ‘greenhouse effect’. The accumulation of GHGs since the industrial revolution has accelerated the greenhouse effect, causing global warming and climate change.
GHGs can be classified into two different types:
- Forcing GHGs: These mainly consist of four gases, namely, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and the fluorinated gases. They take several years to leave the atmosphere and do not react to changes in temperature or air pressure, so they cannot be easily removed.
- Feedback GHGs: These are water vapours. They last in the atmosphere for only a few days. However, they are highly active components of the climate system. They respond rapidly to changes in conditions. They act as feedback to GHGs by circulating the greenhouse effect or by highlighting the warming effect of forcing GHGs.