World Environment Day 2020: Reducing short-lived climate pollutants benefits ecosystems and biodiversity

by CCAC secretariat - 5 June, 2020
Ecosystems and biodiversity are impacted by short-lived climate pollutants in numerous important and sometimes surprising ways. This World Environment Day we call on governments and organisations to reduce air pollution and short-lived climate pollutants to protect biodiversity.

Scientists looking to see how levels of black carbon (soot) pollution in the atmosphere changed over the last century couldn’t rely on historical data, so they turned to the birds. At the turn of the last century to the mid-1900’s the factories in the US Midwest Manufacturing Belt were heavily reliant on coal for energy, turning not just the sky black but the birds as well. By analysing the difference in colour from over 1300 bird specimens, scientists were able to determine that black carbon emissions in the region peaked around 1910 suggesting that black carbon’s historical contribution to climate forcing may be underestimated.

We now know that air pollutants like black carbon are dangerous to human health. Fine particulate matter (PM2.5), of which black carbon is a component, causes 7 million premature deaths a year. This human toll is terrible and must be stopped. Less well understood is the impact of air pollution on biodiversity.

Photos from the study show that birds that lived in heavily polluted areas in the early 1900’s were significantly darker than their modern counterparts (see picture below). What we don’t know is how air pollution impacted their health and behaviour. Birds rely on their plumage to attract mates, defend territory, and for camouflage to escape predators. How a fine dusting of soot affected their survival and evolutionary pathways is still an open question.

This World Environment Day we think about how air pollution impacts biodiversity. Biodiversity is threatened in myriad ways around the world, including through habitat loss, poaching, over consumption, pesticides and chemicals, and plastics and waste pollution. Climate change amplifies these impacts and is helping speed up what scientists are calling the sixth mass extinction event.

Comparison of two Field Sparrows (S. pusilla pusilla), one from 1906 and one from 1996. (Lower) SEM micrographs of belly feathers plucked from the specimens in Upper. SEM micrographs of the Field Sparrow from 1906 show black carbon aggregates composed of small sphericals. The feather from the 1996 specimen lacks black carbon deposition.Both specimens were collected during spring months in the vicinity of Chicago. (DuBay and Fuldner, 2017).

The impact climate is having on eco-systems and biodiversity is happening now and at a startling rate. Bushfires in Australia in 2019 wiped out entire ecosystems in a matter of months. Approximately 10 million hectares (100,000 square kilometres) of land burned, killing over a billion animals and 100’s of millions of insects. The loss of habitat and food sources threatens the lives of millions more. While bushfires are a natural part of Australia’s ecosystem, they are being turbo-charged by a warming climate.

Some air pollutants play an outsized role in both habitat destruction and climate change. Short-lived climate pollutants, like black carbon and tropospheric ozone, are dangerous air pollutants that are many times more powerful than carbon dioxide at heating the planet.

Black carbon poses a serious threat to the ice and snow-covered regions of the world, also known as the cryosphere. The fine black particles caused by burning of bio-mass and dirty fossil fuels like coal, kerosene, and diesel, absorb heat in the atmosphere causing localized warming. When they settle on white snow and ice, they stop these surfaces from reflecting solar radiation and heat back into the atmosphere and instead absorbs this radiation causing melting.

Deposits of black carbon (soot) and dust on snow and ice accelerate melting

In the Arctic, one of the fastest warming regions on earth, black carbon pollution is like pouring fuel on a fire. Black carbon deposits from global air pollution is accelerating the melting of sea ice and glaciers, threatening iconic species like polar bears and walruses, and disrupting the food chain and the entire eco-system. The implications of this are not limited to the Arctic but reverberate globally, in ways that throw other eco-systems into disarray. Increased sea-levels from melted ice erodes and destroys coastal habitats. Changes in Arctic sea ice cover, marine ecosystems, and the water cycle affect the amount of carbon dioxide that the Arctic Ocean absorbs from the atmosphere. The ocean becomes more acidic as it absorbs more carbon dioxide, with potential implications for marine life.

The main sources of black carbon are diesel engines, residential burning of biomass, and oil and gas flaring. In 2017, the Arctic Council set targets to limit black carbon (or soot) emissions to between 25 and 33 percent below 2013 levels by 2025 in a bid to slow Arctic warming. Reducing emissions of black carbon in the Arctic is a major and critical step towards protecting this vulnerable region from climate damages. 

Photo of healthy (top) and ozone-injured (bottom) tulip tree (yellow poplar) foliage.Photo: US National Park Service

Tropospheric (or ground level) ozone is another air pollutant that impacts human health, eco-systems and the climate. Tropospheric ozone is often seen as smog in many cities and aggravates asthma and other respiratory diseases in humans. A recent study in the British Medical Journal found exposure to ground level ozone in cities worldwide is associated with an increased risk of death.

In nature tropospheric ozone reduces photosynthesis, the process that plants use to convert sunlight to energy to live and grow. It stunts their growth and makes them more vulnerable to disease, damage from insects, and harm from severe weather. This harms plant biodiversity and threatens forest ecosystems leading to a loss of species diversity (less variety of plants, animals, insects, and fish). It changes the specific assortment of plants present in a forest, reduces habitat quality, and changes water and nutrient cycles. Its impacts on plants also threatens global food security. Tropospheric ozone is responsible for the loss of over 50 million tonnes of staple food crops annually.

Ozone and methane – the main gas responsible for its formation in the lower atmosphere – are also powerful climate forcers. Planting trees and protecting forests is one a way to help reduce climate change but ozone significantly reduces plants’ ability to sequester carbon further exacerbating the climate crisis, which causes even more harm to ecosystems and biodiversity.

The Climate and Clean Air Coalition is working with governments and partners around the world to help reduce these and other short-lived climate pollutants in order to rapidly reduce the rate of warming in the atmosphere and protect the ecosystems that humans and animals rely on. These powerful climate forcers are in the atmosphere for a relatively short time – from days (for black carbon) to about 15 years (for methane) – and reducing them can quickly flatten the climate curve, helping to prevent the collapse of critical eco-systems, like the Arctic,  and climate feedback loops that could lead to runaway global warming.

The Coalition’s measures can reduce global methane emissions by 45% and black carbon emissions by 60% by 2030. This World Environment Day the Climate and Clean Air Coalition calls on countries to increase their climate ambition through their Nationally Determined Contributions to reduce short-lived climate pollutants in ways that maximise benefits to human health, biodiversity, and the climate.