Significance of 1.5 degree and 2.0 degrees Celsius increase in global temperature

Today, we are witnessing a lively, sometimes acrimonious, debate over global warming. Science, economics and politics are all mixed up in this debate. One of the outcomes of the debate was the 2015 Paris Agreement on Climate Change, where 195 nations agreed to limit the rise in global temperature to 1.5-degree Celsius by the end of this century. Although lauded by some, many scientists have criticised the Paris Agreement because it understates the actual amount of warming predicted by mainstream climate change models. Furthermore, the agreement falls short on addressing the effects of the potency of green house gases and those that are already in the atmosphere.

Any person with a modicum of intelligence knows that even if emissions of greenhouse gases were stopped immediately, the ones that are already present in the atmosphere would continue to raise the global temperature for hundreds of years. That is because, aside from water vapour, the other four principal greenhouse gases―carbon dioxide, methane, nitrous oxide and halocarbons(CFCs/HFCs) can remain in the atmosphere from months to millennia. Consequently, they become well mixed, meaning that their concentration in the atmosphere is roughly the same all over the world, regardless of the source of the emissions.

The potency of a greenhouse gas is determined by what is called the Global Warming Potential (GWP)—a measure of the total energy a gas absorbs over a period of 100 years. The larger the GWP, the more warming the gas causes. With a value of one, carbon dioxide serves as a baseline for GWP of other greenhouse gases. As noted in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), GWP of methane is 28, which means methane will cause 28 times as much warming as an equivalent amount of carbon dioxide. Nitrous oxide has a GWP of 265, while GWP of most of the HFCs, used as refrigerants, is over 1,000.

Another powerful greenhouse gas, sulphur hexafluoride, emitted from a variety of industrial establishments, has a GWP of a whopping 23,500 and an atmospheric lifetime of about 3,200 years. Its atmospheric concentration has increased by two orders of magnitude since industrial production started in 1953.

In view of the long lifetime and large GWP-values of the greenhouse gases, the overwhelming consensus among scientists is that global warming is unstoppable unless drastic measures are taken sooner rather than later. Moreover, as long as carbon based energy consumption continues, global temperature would keep onrising unabated. In a report released in October 2018, IPCC essentially corroborates this assertion by noting that planetary warming is happening faster than the panel’s scientists predicted and the goal of 1.5 degree rise in temperature would happen much earlier than 2100, unless burning fossil fuels is cut by half by 2030. Most climate models, however, predict a rise of 2-degreeor more by 2100.

The difference between 1.5 degree and 2.0 degree may not sound like much, but changes in average temperature of even a degree or less can have big effects on the climate. As we know, a sub-one degree rise in temperature since 1880 has inflicted significant damage to the environment. A 1.5 degree rise will cause even more damage, while a 2.0 degree rise will push our planet into a new, more dangerous climate domain.

The effects on the climate due to the extra half-degree won’t be uniform across the planet. Some regions will heat up faster than other regions. The tropics would experience the biggest increase in the number of unusually hot days. Deserts will become bigger, hotter and drier. Crop yields would be lower, especially in the sub-Saharan Africa, South east Asia, and Central and South America.

Frequency and magnitude of extreme weather events―wildfires, storms, floods, drought and heat waves due to half-degree differential would increase exponentially, as stated in the IPCC report. Additionally, more water would evaporate from the oceans, which in turn would make the heaviest rains and snowfalls even heavier in many parts of the world.

An additional half-degree of warming could mean more melting of ice sheets, resulting in greater habitat losses for polar bears, whales, seals, sea birds and other polar animals. Loss of ice would produce a bigger rise of sea levels.Thus, an extra half-degree of warming could be significant for small island nations, which are particularly vulnerable to sea level rise and other climate change impacts.

Another victim will be the coral reefs, which act as nurseries for many fishes. Almost all tropical coral reefs will be at risk of severe degradation due to temperature-induced bleaching.

According to the latest IPCC report, without aggressive action, many effects noted above and expected only several decades into the future will now arrive by 2040. Hence, the difference between 1.5 and 2.0 degrees Celsius is a big deal!

So, what should we do now? “Do what science demands before it is too late.” This ishow the United Nations secretary General António Guterres admonished world leaders after poring over a recent report prepared by a group of scientists at the request of several small island nations. The report paints a grim portrait of how quickly the Earth is heating up and how serious the consequences would be.

We can reverse, or at least forestall, some of the adverse effects of climate change by appealing to geo-engineering methods. It encompasses two different approaches using a variety of cutting-edge technologies. They are removal and sequestration of carbon dioxide to lower its concentration in the atmosphere and offsetting global warming by blocking some of the solar radiation from everreaching the Earth’s surface via a space-based programme called Solar Radiation Management.

Until geo-engineering technology are fully developed, their environmental impacts tested and subsequently deployed, we have no choice but to use the available technology for non-polluting, renewable sources of energy like solar, wind, geothermal and fuel cells using hydrogen. Many more clean technologies, such as Ocean Thermal Energy Conversion and Hydrokinetic Energy, will become available in the future. In addition, we have to make a clean break with burning fossil fuels. Changing our lifestyle, albeit painful, is a must, too.

Unfortunately, no alarm seems loud enough to penetrate the ears of the world leaders. While nations argue how to implement the flawed Paris Agreement, the United States and Western Europe are still producing carbon dioxide. However, the highest per capita production of carbon dioxide is in the newly industrialised countries. In the present geopolitical environment, it is, therefore, difficult to transform scientific observations into executable policy.

The author, Quamrul Haider, is a Professor of Physics at Fordham University, New York.

Editor’s Note: Sir David Attenborough, the renowned environmentalist, in his speech at the United Nations climate talks in Katowice, Poland in 2018 said, “Right now, we are facing a man-made disaster of global scale. Our greatest threat in thousands of years is the climate change. If we do not take action, the collapse of our civilisations and the extinction of much of the natural world is on the horizon.”


1 thought on “Significance of 1.5 degree and 2.0 degrees Celsius increase in global temperature”

  1. This is a serous topic of global magnitude. But do we really care? Our priorities are different. We possibly believe in ‘ignorance is bliss’.


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