CICERO - Center for International Climate Research
farmers wading in a wet field near karauli in india. Photo: pond5

farmers wading in a wet field near karauli in india. Photo: pond5

Double trouble: Climate change and air pollution

Climate news - News and opinions about climate science

Published 17.04.2018

Smog is already damaging crops in northern India. What  will happen when both air pollution and temperature increase?

– We do not yet fully understand what the impacts of the combined climate and air pollution effects may be for agricultural ecosystems or human health, says Jana Sillmann expert on extreme weather at CICERO Center for International Climate Research.

Sillmann leads the CiXPAG project in which they are looking particularly at a highly threatened region, the Indo-Gangetic-Plain; a fertile plain covering most of northern and eastern India, the eastern parts of Pakistan and virtually all of Bangladesh.

This is a region currently affected by high levels of ozone, and is expected to experience an unprecedented increase in the intensity and frequency of heat waves with climate change.

The Indo-Gangetic-Plain is also the bread- and rice-basket of India, of which a large share of India’s 1.3 billion inhabitants are dependent.

Quarterly GDP growth in India (left) and India’s emissions from 1990 to 2017, by major source. Figures: Robbie Andrew, CICERO

Indias cities, population and economy is growing. Growth means possibilities, but also challenges, some of which are well known: A growing population increases the need for food, while economic growth and higher standards of living will increase emissions and local air pollution.

It is also well known that climate change will affect the region in the form of higher temperatures, as well as increased risk of droughts and extreme rain. But how will climate change and local air pollution affect each other?

– There are many studies that on the one hand look at impacts of climate change and on the other hand the impacts of air pollution on human health or crops. Our understanding of the combined effects from climate extremes, such as extensive heat, and air pollution on human health and crops are very limited, says Sillmann.

– This lack of knowledge is particularly challenging considering the threats that climate change and food security are posing to society, she says.

– We may underestimate the consequences of climate change and increased air pollution levels on crop yield and adaptation measures may not adequately address the challenges of the future

Jana sillmann, CICERO

Haze was pooled along the foothills of the Himalaya Mountains over the Ganges and Brahmaputra Rivers on January 17, 2006. To the north, skies over the Tibetan Plateau were crystal clear, revealing the winter-bare landscape, as well as clear and ice-covered lakes. (Photo: NASA)

 Ozone: Crop killer

– Ozone is a gas that is not emitted; it is formed from other compounds. Nitrogen oxides, carbon monoxide and volatile organic compounds originating from for example cars and factories, reacts with sunlight and forms ozone, says Øivind Hodnebrog climate scientist and expert on ozone at CICERO.

High levels of this gas is harmful to people, and can cause decreased lung function and chest pains. Ozone also reduces crop yields. According to a recent study, high ozone levels caused an annual loss of wheat in northern India of 9 million ton.

That is about seven times the annual production of wheat in the EU – lost to ozone.

The Northern parts of India is a heavily polluted region due to a combination of high population and the Himalayas to the north trapping the air.

Average Ozone-mix in the dry season in India. The green areas are within WHO limit value. The map in the middle shows what can happen under a "very high emission" scenario, and to the right a "high emission" scenario. Figure: How Will Air Quality Change in South Asia by 2050?

– We are expecting an increase in local emissions in this region, as well as we are expecting climate change to bring higher temperatures. Temperature is a known driver for the formation of ozone, says Hodnebrog.

Little wind and high temperatures is also a recipe for heat waves. Earlier studies on the 2007 heat wave in Europe have shown significant increase in ozone levels during these, according to Hodnebrog. 

Knowing the combined effect of climate change and air pollution is essential to successful adaptation according to Sillmann:

– More research is needed on understanding and modeling the combined effect of climate change and air pollution to better inform decision-makers.

– We may underestimate the consequences of climate change and increased air pollution levels on crop yield and adaptation measures may not adequately address the challenges of the future, she says.


Good Ozone and Bad Ozone, (From

Good Ozone

Called stratospheric ozone, good ozone occurs naturally in the upper atmosphere, where it forms a protective layer that shields us from the sun's harmful ultraviolet rays. This beneficial ozone has been partially destroyed by manmade chemicals, causing what is sometimes called a "hole in the ozone." The good news is, this hole is diminishing. Learn more about Stratospheric, or "good" ozone.  

Bad Ozone

Tropospheric, or ground level ozone, is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC). This happens when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources chemically react in the presence of sunlight. Ozone at ground level is a harmful air pollutant, because of its effects on people and the environment, and it is the main ingredient in “smog." Learn more about air emission sources.

Ozone is most likely to reach unhealthy levels on hot sunny days in urban environments, but can still reach high levels during colder months. Ozone can also be transported long distances by wind, so even rural areas can experience high ozone levels.