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  • Writer's pictureRuwan

The Deep-Dive Series, part 1: What is global dimming & why should we care?

Updated: Aug 4, 2020

As we all work from home, worry, set up our temporary offices, snack, snack, and proceed to worry some more, we figured that some folks may have a little more time for reading, so we’ve curated a few ‘science-heavy’ blog posts to keep you occupied during these strange times… because if one thing’s for sure, once we have gotten out of our COVID-19 mess, climate change will remain one of the greatest challenges we face as humanity.

We will be releasing a four-part in-depth series to share knowledge on some really important climate issues that we typically see under-reported; global dimming, tipping points, habitats & health, and a pick of our favourite pieces of tech-based climate change solutions. These issues are all interrelated, so we hope you are able to enjoy them as a series over the coming weeks. A little basic understanding of climate change will help you, and there’s a great video for you here on that.

So, here’s our first article for you - everything you need to know about ‘Global Dimming’, the cooling effect caused by certain atmospheric pollutants...

Due to the COVID-19 outbreak, industry is shutting down in various parts of the world and air pollution is decreasing as a result. Data has been collected about the concentration of air pollutants before and after countries were forced to implement lockdowns due to COVID-19.

The European Environment Agency (EEA)’s data for recent weeks show how concentrations of nitrogen dioxide (NO2), a pollutant mainly emitted by road transport, have decreased in many Italian cities. For example:

  • In Bergamo, there has been a constant decline in NO2 pollution over the past four weeks. The average concentration during the week of 16-22 March was 47% lower than for the same week in 2019.

  • In Rome, average NO2 concentrations for the past four weeks were 26-35% lower than for the same weeks in 2019.

We have seen many articles recently around how COVID-19 presents an opportunity for the climate to recover from the harmful effects of human activities. Whilst of course it is absolutely vital for us to reduce CO2 emissions, we are unlikely to see the reduction in global temperatures that we would all hope to see, in-fact, temperatures could increase. This is due to the phenomenon known as ‘global dimming’...

We recently spoke to Singapore-based climate scientist Professor Jeff Obbard about this, who had some incredible insights to share with us on the topic.

As most of us know, burning fossil fuels releases greenhouse gases along with harmful particles into the atmosphere. The gases act as a blanket, steadily causing the atmosphere to warm - it’s as if we had created a greenhouse around the world (hence ‘greenhouse gases’). Climate scientists have been warning the world that we need to reduce overall emissions in order to prevent global warming - a catastrophic temperature rise that would make life on earth much harder for humans to endure; destroying ecosystems, causing an increase in natural disasters, and rising sea levels.

Greenhouse gases are not created equal… Some last longer than others in the atmosphere, some are more powerful and some have effects other than warming. Whilst the majority of our focus on greenhouse gases tends to revolve around carbon dioxide (CO2), there are other gases and particles released when we burn fossil fuels - whether that’s through the engines powering our cars, or the oil burned by large power stations.

And here’s the strange part, some of the particles actually have a short-term cooling effect on the earth, also known as ‘global dimming’.

Global dimming is thought to have been caused by an increase in aerosol particles, such as sulphate aerosols in the atmosphere, due to human action. Global dimming creates a cooling effect through reflecting some of the sun’s heat, reducing the average temperature rises from greenhouse gases by 0.2–1.1°C, with the IPCC referring to a median of 0.5°C. So, while the release of CO2 through burning fossil fuels is contributing to the warming of the planet, the simultaneous release of aerosol particles is cooling it, ultimately masking some of the true effects of excess CO2 emissions. The phenomenon has interfered with the hydrological (water) cycle by reducing evaporation, and this may have caused reduced rainfall in some areas.

As Professor Obbard puts it, 'As we attempt to reduce short-lived atmospheric particulates to protect human health we must also simultaneously reduce the overburden of long-lived carbon dioxide, if we are going to avoid the impact of rapid temperature increases from lowered global dimming.'

It is the ultimate paradox. Without this particle-masking effect, warming effects would be much higher. We know that carbon dioxide is a long-lived greenhouse gas, remaining in the atmosphere for decades to come, which means that if we managed to achieve 0 emissions today, the effects of CO2 wouldn’t simply disappear. However, global dimming particles in the atmosphere are short-lived pollutants, so if the source is reduced, the particles would start disseminating from the atmosphere in days or weeks, ultimately removing the cooling effect counteracting the warming caused by the carbon dioxide in the atmosphere.

This means that as pollutants decrease in-line with covid-19 related reductions in travel and industry, we could expect a rise in temperatures.

Evidence of this can be found in what followed the September 11 attacks in New York City in 2001. After the attacks on the World Trade Towers, air traffic was grounded for 3 days, the consequence of this being reduced aircraft-related pollution in the upper atmosphere and a reductions in particles shading the United States. Within a week, the US experienced an increase of land-based average temperatures. Short-term reductions of emissions resulted in a rise in temperatures, as the cooling effect could no longer reduce the warming caused by atmospheric CO2.

On July 16, 1990, a magnitude 7.8 earthquake (comparable in size to the great 1906 San Francisco, California, earthquake) struck about 60 miles (100 km) northeast of Mount Pinatubo on the island of Luzon in the Philippines, shaking the Earth's crust beneath the volcano. Nearly 20 million tons of sulphur dioxide were injected into the atmosphere in subsequent volcanic eruptions. The dispersal of this gas cloud around the world caused global temperatures to drop temporarily (from 1991 through to 1993) by about 1°F (0.5°C).

Climate scientists had been confused around why the world wasn’t experiencing warmer temperatures as a result of global warming, until it was determined that global dimming was in play...

I know what you’re thinking, or at least I know what I’m thinking... We are supposed to reduce carbon emissions in order to prevent complete breakdown, but doing so would cause some shading particles to disperse, reducing the cooling effect, resulting in temperatures rising further...are we sure this is the right action to take? As Professor Jeff put it; it is “the impossible, unsolvable paradox, as we attempt to reduce greenhouse gas emissions, lower global warming potential, but also reduce the burden of particles in the atmosphere, which will increase the warming.”

So, scientists certainly are interested in the effect of COVID-19 on the climate, as countries around the world begin enforcing stay-at-home measures and the shutting down of their industries. But instead of a ‘slow down’ of climate change, we are expecting a short-term additional rise in temperatures... observing the effects of cooling particles dropping from the atmosphere and we fully start to experience the effects of uninhibited CO2.

Will this cause us to start taking united and meaningful action against climate change sooner? We sure hope so.


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