March 1, 2021

I, Science

The science magazine of Imperial College

As the climate changes, we take a look at the consequences of an unchecked rise in temperatures ...


In the absence of any policy changes, the global temperature in 2100 will be 4 °C higher than in pre-industrial times. That may not sound like much, but according to climate scientists and recent reports from the IPCC and the World Bank, there will be dramatic consequences. World Bank president Jim Yong Kim has said that “[l] ack of action on climate change threatens to make the world our children inherit a completely different world.” So just how will the world change?

While the average global temperature increase will be around 4 °C, this temperature change won’t be distributed evenly across the world. Among the most impacted regions will be the polar ice caps. The temperature in the Arctic is rising at approximately double the global average rate, which has led to a 40% decrease in sea ice over the past 30 years. As the ice caps melt, they release water into the oceans, diluting the oceans and leading to rising sea levels.

The surface of the sea is not level around the globe. The polar ice sheets, mountains and deep sea vents all perturb the pull of gravity, leading to ‘mountains’ and ‘valleys’, which are further shaped by the effects of wind and ocean currents. The Gulf Stream, for example, pulls water away from the north-eastern USA, leading to a lower sea level. These currents are driven by ‘thermohaline gradients’ – differences in temperature and salt levels. As the polar ice caps melt, cold water will be added to the oceans, disrupting these gradients. If the Gulf Stream is disrupted, the local sea rise will be higher around the north-eastern USA than elsewhere. There will also be large rises around Asia and Africa.

Sea levels could rise by as much as two metres by 2100, meaning flooding will increase and many coastal cities and small island nations could be lost. Bangladesh is prone to floods, containing 230 rivers that swell during monsoons. With rising sea levels and increased rainfall, the country could find itself completely changed. If sea levels rise by 1 metre, a quarter of the coastline could be lost, with 30 million people losing their homes.

In addition to the Arctic getting warmer, hot regions will get even hotter, leading to droughts and water shortages in many parts of the world. Land temperatures will rise more than ocean temperatures, meaning a greater overall impact than the quoted 4°C rise suggests. It has even been suggested

that, just as wars in the 20th century were fought over oil, wars in the 21st and 22nd centuries could be fought over water.

As well as shifts in the average temperatures, there will also be changes to weather patterns. What we currently think of as extreme weather – the recent never-ending winter or the heat waves that affected much of Western Europe in 2003 and killed around 55,000 people in Russia in 2010 – will become more and more common. Heat waves in Australia in 2009 put power supplies and morgues under tremendous stress, while railway lines in Adelaide buckled under the heat. As well as increased heat waves, tropical cyclones are likely to increase in both frequency and intensity thanks to the changes in ocean temperature.

Droughts, increased temperature and changes to weather patterns are likely to have huge impacts on agriculture, ecology and biodiversity. During the 2010 Russian heat wave, approximately 25% of crops failed, leading to $15 billion in economic losses. Crop failures due to droughts in the USA in 2012 led to food price increases on a global scale.

Sea life will be affected both by changes to the ocean temperature and to its chemistry. As more carbon dioxide is produced, the ocean will become more acidic. Its pH is predicted to decrease by approximately 0.3 compared to pre-industrial levels (a lower pH means greater acidity); this is a bigger drop than it sounds, since pH is a logarithmic scale. As pH drops, the calcium carbonate that makes up shells is more easily dissolved. Populations of many corals, molluscs and other marine wildlife have already been hit by climate change, and this situation will only get worse as ocean acidification continues.

Other ecosystems such as the Amazon rainforest will also be affected by forest fires, death of plants, extreme rainfall and droughts. The Amazon is one of the largest ‘carbon sinks’ on Earth, containing a whopping 100 billion tonnes of carbon. However with deforestation and forest fires, the Amazon could switch from sink to source, producing carbon dioxide and exacerbating climate change.

The World Bank and the IPCC currently have a target of cutting the temperature rise to 2 °C by 2100. With current policies and pledges we are on course for a 4 °C rise. Reaching the target will require dramatic cuts in greenhouse gas emissions, something which most governments seem reluctant to do.

Although most scientists and politicians are in agreement that man-made climate change is a major problem, there is a reluctance to act for fear of inhibiting economic growth, particularly in the current economic climate. However, while there will be short-term savings to be made by maintaining the status quo, failure to act on climate change could lead to far greater economic damage in the future. According to a 2005 study, acting to prevent climate change will cost the USA approximately $12 trillion by 2100, but inaction will lead to damage costing around $20 trillion by 2100 and over $70 trillion by 2200.

Politicians may be worried about the fragile economic climate, but there is another climate to worry about – one which seems in an even more perilous position and will change irrevocably unless action is taken.


IMAGE: Shaunamy