Global dimming — more dangerous than global warming?

Salt Lake City smog and haze

Smog and haze hangs over Salt Lake City in this 2016 image. (Eltiempo10/Creative Commons 4.0)

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Climate, Past Storyfest Entries

Imagine waking up to a world, where the climate is reversed, the global north becomes warmer, and the global south becomes cooler. It may seem like a wildly disturbing possibility, wherein decreasing levels of air pollution, thanks to effective climate policies, would result in a rapid increase in global warming. Yes, you read it right, a rapid increase.

It may happen that the very measures we are hoping to tackle climate change with, could result in the opposite, bringing more misery than respite. In such a scenario, many questions might arise in your mind: Can we trust the scientific community? Is there really no solution to the climate crisis? Do we need more air pollution to delay the warming of the planet? Are we looking at another ice age? (Thankfully not. Another ice age may happen but a 100,000 years later.) But global dimming and global warming are happening right now. How is that even plausible? Well, the only way to find a way out of this labyrinth of confusion and paradoxical claims, is to understand the phenomena of global dimming. As it sits, right under our nose, a distant cousin of global warming, that not many talk about.

This silence on global dimming could be detrimental to the way we devise climate policy, and it will definitely change how we imagine our future in a rapidly warming, or even a rapidly cooling world. Planet Earth has a sensitive climate, where even a small change in the atmosphere can trigger dangers for human beings. Some of these impacts already have taken place in the form of cyclones, volcanic eruptions, floods, and earthquakes. We have not only normalized environmental destruction, both in the ways we get affected by it and in the way we cause it — but also by adding the drama of global dimming to this soup. This might not raise many eyebrows, but that doesn’t mean we shouldn’t be scared, because there is so much about our planet that we have yet to discover. The climate is one of the most complex systems on Earth, even when we say it is changing rapidly, it is not doing so within seconds. The impact that it can have on life, will make or break our future within seconds.

This uncertainty shouldn’t be the cause of fear, rather the start of an acceptance, toward a world, where the more we try to stake a claim, the more we have to lose, both in resources and in lives. The ongoing global pandemic is the latest result of this uncertain future that has been passed on to us. Under normal conditions, the sun, our only source of heat, emits solar radiation. About 26% of the incoming solar radiation is reflected back into space by the atmosphere and clouds. Only 19% is absorbed by the Earth. This incoming radiation or insolation is of shorter wavelengths compared to the outgoing solar radiation which is of longer wavelengths. This process of giving and take forms a balance called the heat budget, without which extreme temperatures would cause excessive cooling and warming on the planet. When aerosols enter the atmosphere, just like clouds they also reflect back the incoming solar radiation into space, acting as a reflective piece of mirror. Due to this the heat budget or balance gets destabilized. This results in the cooling of the Earth and causes a new kind of climatic change called global dimming. Aerosols are basically fine solid particles or liquid droplets. They can be both naturals, as well as anthropogenic like fog, mist, dust particles, fossil fuel emissions, even deodorant sprays, and volcanic ash, which are all nothing but an aerosol, some significant contributors to air pollution.

Global dimming is, therefore, a decrease in the amount of solar radiation reaching the surface of the Earth. The byproducts of fossil fuels in the form of aerosols are the ultimate enemy of the planet here. This phenomenon of dimming was first observed in the 1950s when Gerald Stanhill, an English scientist working in Israel, studied the decline in a few scientific papers and coined the term global dimming, and even then, the larger scientific community failed to take notice or make much uproar about the issue. Measurements from the 1960s to the early 1990s backed up by a range of data and independent studies proved the global phenomenon. But some say that the issue goes way back to 1783 when a volcanic eruption in Iceland made scientists sit up to the possibility of smoke and ash blocking sunlight and causing unusually cold weather in Europe. The connection was made clearer in the 20th century, on whether a human volcano of Air pollution might cause similar changes or not. Surprisingly this change in Iceland even led to the most catastrophic famine in the history of the nation. During World War – II the new field of aerosol science was developed to understand the spread of aerosol particles from wartime explosions, to understand their impact on climate. On similar lines, some scientists warned that a nuclear war could lead to nuclear winter and even linked the extinction of dinosaurs with Global Dimming. Blaming it for cooling the atmosphere and leading to their demise. But the clearest evidence came when Mount Pinatubo in the Philippines suddenly erupted, releasing 20 million tons of Sulfur Dioxide into the air, creating a lingering haze of Sulfate Aerosols. This event was investigated by NASA scientists led by James Hansen, who deduced that half a degree drop in global temperatures, especially in the Northern Latitudes was to be expected in the coming decade as a result of this eruption. And that is what exactly happened, convincing the scientific community by the Mid 1990s that Global Dimming cannot be ignored anymore.

All this hue and cry for a phenomenon that has been observed in almost all parts of the world today was just limited to the Global North back then, maybe due to the rapid advancements in Industrialization and Urbanization. It was not until the 1960s, that a cumulative mixture of Industrial Pollution, haze, smog, and shifting cultivation (Slash and burn agriculture) finally made the Global South bear witness to Global Dimming too. Closer home an Indian scientist, Dr. Veerabhadran Ramanathan has documented how pollution was severely dimming areas of the Indian Ocean. In the famous study called Project INDOEX, he found that a huge brown ash cloud generated from the pollution streams, traveling airborne over the Indian ocean from India onto the Northern and southern ends of Maldives were a cause of concern. These streams were creating a nearly three km thick layer made of toxic aerosols that were blocking the sunlight reaching the ocean. Therefore, with mounting evidence, NASA launched a satellite called “Aqua” in 2002 which gathered satellite data confirming that aerosol pollution was cooling the climate by more than a degree Celsius. One can understand from this that the warming of the Planet due to Global Warming, is consistently being offset by the cooling effect from Global Dimming.

It has also been theorized that today’s rapid climate change may increase Volcanic activity, since 2000, on average the world has witnessed, around 60 to 80 volcanic eruptions every year. According to a recent study by a team of researchers that analyzed volcanic fallout records in six Arctic ice cores, found that one of the largest volcanic eruptions of the past 2,500 years occurred in early 43 B.C.E. and it was among the coldest years of the recent millennia in the Northern Hemisphere at the start of one of the coldest decades. Further research suggested that this high-latitude eruption led to pronounced changes in hydroclimate, including colder seasonal temperatures in specific Mediterranean regions during the two-year period following the eruption, thus the link between volcanic eruptions and cooling on account of Global dimming may be having a longer history than anticipated.

From the face of it, one thing is clear, that Aerosols are the major cause of Global Dimming. While we cannot rule out the possibility that natural variations in the Earth’s climate may have contributed to this, but the effects are so closely related to Air pollution that human activity seems to be largely responsible. Thus, Pollution from millions of vehicles and Airplane contrails (those white streams of vapor filled clouds coming out of the back of the airplane), not only causes Global Warming, but also Global Dimming. Thus, it is not only the intensity of polluted air but also the composition of polluted particles in the air that should matter. Global Dimming has three-fold economic, environmental, and social implications. It can affect the Solar energy Industry, as lack of sunlight will lead to delay in charging of solar power-dependent units, the environmental costs in terms of agricultural productivity and acid rain are also going to cause damage in certain areas, ultimately causing social distress, unrest, and diseases that are respiratory in nature, much of which seems to be already unfolding.

Globally Dimming has already been observed in areas like Hong Kong, China, India, Chile, and Venezuela. Whereas almost 22 sites in both Arctic and Antarctic have observed dimming. There have been gaps in observations over Africa, South America, and Maritime continents. Not enough studies have focused on the impact on the Ocean surface except for a few island studies. Overall, the southern hemisphere seems to be better off compared to Northern Hemisphere which has seen around 4 – 8 percent dimming. In the Global North, Europe and North America are recovering faster than China and India, where Global dimming is still on the rise. Global Dimming can also lead to changes in the Rainfall pattern. It has caused Water in the Northern Hemisphere to become colder, which means slow evaporation and fewer water droplets. This in return reduces the amount of Rain reaching worldwide, which is a cause of concern for the Asian Monsoon responsible for 50 percent of the world’s annual rainfall. This leads to a weakening of the monsoon and associated increased droughts over India. It had already been established that the drought and famine of the Sahel which has killed thousands of innocent people in sub-Saharan Africa during the 1970s, was largely due to global dimming. If this happens again, then half of the world’s population will be starving. Not only this it is also believed to cause heatwaves and runaway fires.

Also, a decrease in sunlight or solar radiation will negatively impact the process of photosynthesis in plants. Along with Sahel’s famine and drought, the 2011 Ethiopian Food crisis has also been linked to dimming. A 2007 NASA sponsored satellite-based study sheds light on the puzzling observations by other scientists that the amount of sunlight reaching Earth’s surface which had been steadily declining in recent decades, began to reverse around 1990. This switch from a “global dimming” trend to a ” global brightening” trend happened just as global aerosol levels started to decline in the atmosphere, due to strict policy measures taken in the Global North. A specific look at India suggests a grim scenario with a 6.3 percent decline per decade for the national capital. The annual daily bright sunshine duration now stands at about 7.5 hours, down by nearly an hour from around 8.4 hours in 1971.

Activities like biomass burning and open burning of crops are causing dimming. It has been linked with the spread of urban areas and industrial activity in all metros and in fast-developing cities such as Nagpur and Pune. Delhi is influenced by heavy injection of dust load blown over from deserts in the western parts of the country, particularly during pre-monsoon season. Delhi and parts of North India also get dust particles transported from Sahara as well. There might still be some time before we say a final goodbyes to sunshine altogether, even though the problem has not surfaced much again in Westernized Europe and America, the East is still being impacted by Global Dimming. Sometime in the future we may see strict Air pollution regulations in East Asia and India which are quite inevitable, and with the Pandemic, we can already observe the short term positive impact it can have on our environment, with lesser traffic and industrial activity, but on the other hand, decrease in aerosol layers in the atmosphere will allow more sunlight and naturally more heat in the environment, accelerating Global Warming and Climate change.

Therefore, in the long run, a turn to Global brightening can be expected but this should be accompanied by a reduction in Green House gas emissions as well if we want to tackle both the problems at once. It is due to both global warming and global dimming that earth’s temperature has increased less than what it should have been. Without global dimming, this planet is too warm for all of us to survive. Both of them are dangerous and can prove fatal for our environment and need to be solved together. Solving each problem at a time could create worse conditions. China, Indonesia, and India have been contributing a lot more of the particulates and aerosols which produce dimming. Regionally, they are experiencing dimming at the levels that North America and Europe were in the 1960s and 1970s.

The problem hasn’t gone away, but it has shifted locations quite a bit. It is a welcome sign that the developing countries in the world are changing their energy mixes to renewables rapidly and realizing that pollution is killing their people and slowing their economies. China and India are both shutting down coal plants, putting a halt to new coal construction, and building a ton of wind and solar. China is also building a fair amount of nuclear as well, which is much, much better than building more coal generation. Global dimming will be much reduced over the coming decades.

There will still be airplane contrails, forest fires, volcanoes, and the like to deal with, but this is much closer to natural levels. If even this threat doesn’t make human beings stop the consumption of fossil fuels, then perhaps we surely are going to wake up to a world, where not only the climate is reversed, but also our fate. Humanity may be looking at its last chance to redeem itself from all that is yet to come, and sometimes it is good to be scared, for it is only when we are scared, that we truly come together to solve the greatest problems in the world, a pandemic, or maybe another extinction? Who knows?


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5. BBC Horizon Documentary on Global Dimming

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