Our world is getting hotter with each passing day. July 2018 was one of the warmest months ever recorded, and the July temperatures have been higher almost everywhere on our planet in the past 10 years. Scientists have already warned that we must limit global temperature rise to 1.5 degrees to avoid the worst impacts of climate change. That’s compared to the temperatures in 1850-1900, before widespread industrialization.

The earth has already warmed about 1℃ since then. That may hardly sound like much, but if countries fail to act to limit warming, our world could face a ‘catastrophic change’. Sea levels will rise, risking the displacement of hundreds of millions of people. We will also face more extreme weather phenomena such as droughts, heat-waves and heavy rains, and our ability to grow crops like rice, maize and wheat will be in danger.

If global warming continues at today’s rate, temperatures may rise by 3-5℃ before the century ends.

Why warming?

Such a climactic change has been attributed to systems on and beyond Earth. Our planet has always experienced changes in climate, but they have occurred due to natural changes like changes in the angle of Earth’s axis, Earth’s orbit around the Sun or solar radiation. Natural changes still take place on planet Earth.

However, they hardly contribute a fraction to the current climatic crisis.

One of the culprits is the use of fossil fuels, which has greatly increased after the Industrial Revolution. The combustion of fossil fuels raises the concentration of greenhouse gases, like CO2, in the atmosphere; this increase contributes to producing a warmer climate. Measurements show that temperatures have risen throughout the world and that the average temperature in the Arctic has risen twice as rapidly in the past 100 years as it has elsewhere in the world.

The reason for this is the complex feedback loops between the atmosphere, the oceans, and the ice. Therefore, it is difficult to predict how quickly the changes will take place; so far, they have occurred more rapidly than most scientists predicted.

Measurements reveal that the temperature over the land has risen more than in the sea, and that this rise has been the greatest in winters. Climate models — which calculate the future trend in the climate — show that temperatures will continue to rise, and the increase will be about 3-5°C over land and up to 7°C over the oceans before the turn of the century. Winter temperatures are expected to rise even more.

Warming waters

Estimates by experts have found that the oceans were taking up around 8 zeta-joules of energy each year — that’s an ‘8’ followed by a whopping 21 zeros! Our research, though, put it at around 13 zeta-joules. According to the International Energy Agency, the total energy consumption worldwide is around half a zeta-joule annually. This suggests that our planet, as a whole, is more sensitive to climate change than previous estimates implied. This indicates that the planet may respond more strongly to future greenhouse gas emissions than expected.

This may have some grave implications for global efforts to meet the climate targets outlined under the Paris Agreement. Currently, nations are striving to keep global temperatures within 2°C of their pre-industrial levels, or a more ambitious 1.5°C if possible. Just last month, the panel released a much-anticipated report on the 1.5°C threshold, concluding that meeting the target would need an unprecedented effort from world leaders and net-zero carbon emissions by 2050.

If our planet is more sensitive to climate change than previously thought, those temperature targets could be met more quickly. That means nations may have to work harder or cut emissions more quickly to stay on track. In fact, one study suggests that the maximum amount of emissions humans could still emit without overshooting the Paris targets would need to be reduced by about a quarter.

The carbon choking: the ocean heat content and CO2 concentration measurements since the 1950s. The black line represents ocean heating for the upper 2,000 meters of the ocean, and light red shading represents the 95 per cent confidence interval. The CO2 concentration observed in the Mauna Loa Observatory is displayed by light blue. Image courtesy: Lijing Cheng

In the past decade, scientists have significantly beefed up a large global network of ocean floats — part of an international program known as ‘Argo’ — that measures temperature and salt content. But before 2007 or so, ocean floats were much sparse, and scientists also widely relied on measurements taken by passing ships. That made it a little difficult to estimate ocean changes throughout the world because these data tended to be concentrated mainly in major shipping routes.


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