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Global Trends of CO₂ and other Greenhouse Gas Emissions

Carbon dioxide (CO2) is known as a greenhouse gas (GHG)—a gas that absorbs and emits thermal radiation, creating the ‘greenhouse effect’. Along with other greenhouse gases, such as nitrous oxide and methane, CO2 is important in sustaining a habitable temperature for the planet: if there were absolutely no GHGs, our planet would simply be too cold. It has been estimated that without these gases, the average surface temperature of the Earth would be about -18 degrees celsius.1

Since the Industrial Revolution, however, energy-driven consumption of fossil fuels has led to a rapid increase in CO2 emissions, disrupting the global carbon cycle and leading to a planetary warming impact. Global warming and a changing climate have a range of potential ecological, physical and health impacts, including extreme weather events (such as floods, droughts, storms, and heatwaves); sea-level rise; altered crop growth; and disrupted water systems. The most extensive source of analysis on the potential impacts of climatic change can be found in the 5th Intergovernmental Panel on Climate Change (IPCC) report; this presents full coverage of all impacts in its chapter on Impacts, Adaptation, and Vulnerability.2 In light of this evidence, UN member parties have set a target of limiting average warming to 2 degrees celsius above pre-industrial temperatures.

This entry provides a historical to present day perspective of how CO2 emissions have evolved, how emissions are distributed, and the key factors that both drive these trends and hold the key to mitigating climate change.

To set the scene, let’s briefly look at how the planet has warmed — particularly since the Industrial Revolution. In the chart below the x-axis shows the time spanning 1850 to 2018. On the y-axis, we see the global average temperature rise above or below the 1961-1990 baseline temperature. This means that we use the average temperature over the 1961-1990 period as a baseline against which yearly changes in temperature are measured.

The red line represents the average annual temperature trend through time, with upper and lower confidence intervals (the possible upper and lower range) shown in light grey. We see that over the last few decades, temperatures have risen sharply at the global level — to approximately 0.8 degrees celsius higher than our 1961-1990 baseline. When extended back to 1850, we see that temperatures then were a further 0.4 degrees colder than they were in our 1961-1990 baseline. Overall, if we look at the total temperature increase since pre-industrial times, this therefore amounts to approximately 1.2 degrees celsius. We have now surpassed the one-degree mark, an important marker as it brings us more than halfway to the global limit of keeping warming below two degrees celsius.

In the interactive chart below you can also view these trends by hemisphere (North and South), as well as the tropics (defined as 30 degrees above and below the equator). Here we see that the median temperature increase in the North Hemisphere is higher, at closer to 1.4 degrees celsius since 1850, and less in the Southern Hemisphere (closer to 0.8 degrees celsius)…[ ]

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Posted by Gerrym

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