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Global warming is the rapid increase in the Earth’s average surface temperature over the past century primarily due to greenhouse gases (GHGs). It occurs when GHGs collect in the atmosphere and absorb sunlight and solar radiation that have bounced off the Earth’s surface. Normally, this radiation would escape into space, but these GHGs trap the heat in the atmosphere and cause the planet to get hotter. Since 1850, almost all the long-term warming can be explained by GHGs and other human activities.

Carbon dioxide accounts for the largest percentage of greenhouse gases (76%), followed by methane (16%), and nitrous oxide and fluorinated gases (8%). The carbon cycle has both emissions sources and carbon sinks, and their difference is the atmospheric growth (see the figure below for the 2009-2018 averages).

Greenhouse Gases

There is a strong correlation between rising temperatures and an increase in carbon dioxide concentration in the atmosphere. All 19 years since 2001 rank among the 20 warmest years since measurements began (1880), with 2019 the second-warmest year of all time. The effects of global warming include extreme weather events such as heat waves, droughts, wildfires, floods and hurricanes. 

While these types of events may pose only temporary disruptions, global warming is also causing geographical changes that pose a permanent threat to our planet.

S&P Global Platts Analytics estimates global GHG emissions are expected to drop 5.5% this year due to fallout from the Covid-19 pandemic. While that is significant, it still falls short of the 7.6% each year in reductions that the UN Environment Programme (UNEP) says the planet needs to keep global warming below 1.5 degrees Celsius under the Paris Agreement.

According to the UNEP Gap Report published last year, in order to limit the temperature rise to 1.5 degrees Celsius, global emissions must drop rapidly to 25 gigatons of carbon dioxide equivalent (Gt CO2e) by 2030; however, based on current climate commitments under the Paris Agreement, emissions are on track to be 56 Gt CO2e in 2030, over twice what they should be. The full report can be found here and a summary of the report can be found here.

A carbon footprint is the total GHG emissions caused directly and indirectly by an individual, organization or an event. It is calculating by summing the GHG emissions over the life of a product or a service – from manufacturing to delivery to use or consumption. The global warming potential of each GHG (its ability to trap heat) is expressed in units of carbon dioxide equivalents – CO2e. A typical U.S. household has a carbon footprint of 48t CO2e per year. You can calculate your carbon footprint at