Greenhouse Gases from human activities are the most significant driver of observed climate change since the mid-20th century.
For most of the past 800,000 years—longer than human civilization has existed—the concentration of greenhouse gases in our atmosphere was between about 200 and 280 parts per million. (In other words, there were 200 to 280 molecules of the gases per million molecules of air.) But in the past century, that concentration has jumped to more than 400 parts per million, driven up by human activities such as burning fossil fuels and deforestation.
Identified by scientists as far back as 1896, the natural warming of the earth that results when greenhouse gases in the atmosphere trap heat from the sun --that would otherwise escape into space-- creates what is called the greenhouse effect. To quote from the NRDC, this is a good thing until it isn’t. It warms the planet to its comfortable average of 59 degrees Fahrenheit (15 degrees Celsius) and keeps life on earth, well, livable. Without it the world would be a frozen, uninhabitable place, more like Mars. The problem is, mankind’s voracious burning of fossil fuels for energy is artificially amping up the natural greenhouse effect.
Sunlight makes the earth habitable. While 30% of the solar energy that reaches our world is reflected back to space, approximately 70% is absorbed by the land and the oceans (often called “carbon sinks”, with the rest being absorbed by the atmosphere, heating our planet. This heat is then radiated back up in the form of invisible infrared light. While some of this infrared light continues on into space, the vast majority—indeed, some 90% —gets absorbed by atmospheric gases, known as greenhouse gases, and is redirected back toward the earth, causing further warming as it creates “the greenhouse effect”.
The result? An increase in global warming that is altering the planet’s climate systems in countless ways.
The extreme weather. The melting glaciers. The weirdly warm oceans. They’re all the product of global warming, which is being driven by the release of the three most important heat-trapping gases: carbon dioxide, methane and nitrous oxide. And, according to a new study from the National Oceanic and Atmospheric Administration, atmospheric concentrations of those three greenhouse gases continued to surge last year to historic highs.
Carbon dioxide (CO2) enters the atmosphere through burning fossil fuels (coal, natural gas, and oil), solid waste, trees and other biological materials, and also as a result of certain chemical reactions (e.g., manufacture of cement). It can also be emitted from the landscape through deforestation, land clearance for agriculture or development, and degradation of soils. About 76% of global human-caused emissions sticks around for quite a while. Once emitted, 40% still remains after 100 years, 20% after 1,000 years, and 10% as long as 10,000 years later.
Methane (CH4) is emitted during the production and transport of coal, natural gas, and oil as well as resulting from livestock, other agricultural practices, land use & decay of organic waste in municipal landfills). Agriculture is the biggest source (40%). While super-polluting greenhouse gas emissions like methane don’t last in the atmosphere as long as CO2 (living decades rather than centuries), they do plenty of damage while they’re hanging around, accelerating the pace of global warming. A United Nations study issued in May, 2021 suggested that focusing on methane reductions from fossil fuels activities, landfills and agricultural production could help avoid almost 0.3 degrees Celsius of warming by the early 2040s.
Nitrous oxide (N20) is emitted during agricultural, land use, industrial activities, combustion of fossil fuels and solid waste, as well as during treatment of wastewater. It is largely the result of nitrogen fertilizer and manure used in agriculture.
Chlorofluorocarbons (CFCs) are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes.
Water Vapor is the most abundant greenhouse gas, but because the warming ocean increases the amount of it in our atmosphere, it is not a direct cause of climate change.
Reducing carbon dioxide emissions will require radical overhauls to our energy and transportation systems. Drawing down methane and nitrous oxide emissions will mean fundamentally overhauling how food is produced.
Each of these gases can remain in the atmosphere for different amounts of time, ranging from a few years to thousands of years. They all remain long enough to become well mixed, meaning that the amount that is measured in the atmosphere is roughly the same all over the world, regardless of the source of the emissions.
Some gases are more effective than others at making the planet warmer and “thickening the Earth’s blanket.” The EPA has that covered as well.
CREDIT: EPA
As greenhouse gas emissions from human activities increase, they build up in the atmosphere and warm the climate, pushing the planet into unprecedented territory, ravaging ecosystems, raising sea levels and exposing millions of people to new weather extremes, not to mention accelerating disease and extinction to all forms of life. At the current rate of emissions, the world will burn through its remaining “carbon budget” by 2030 — putting the ambitious goal of keeping warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) irrevocably out of reach.
The latest IPCC report (3/20/2023) suggests that the world is running out of options to hit climate goals. Governments, businesses and individuals must summon the willpower to transform economies, embrace new habits and leave behind the age of fossil fuels — or face the catastrophic consequences of unchecked climate change.
During the first Trump administration, U.S. action around most super pollutants (with the exception of nitrogen oxide) came from states and cities, with the cooperation of some industry associations. That changed under the Biden administration, although even there, change was difficult, as was demonstrated, for example, when the Build Back Better bill, the most sweeping climate bill in U.S. history collapsed in December 2021, after coal-state Sen. Joe Manchin III (D-W.Va.) pulled his support. Still, in August 2022, the Biden Administration signed the Inflation Reduction Act (IRA) into law, expanding tax credits for renewable energy projects such as wind, solar, and geothermal and for purchasing electric vehicles, supporting clean energy projects, and providing rebates and incentives for homeowners to improve energy efficiency. In 2021, the DOE committed $35 million for technologies to reduce methane, and the EPA announced a phase out of HFCs. On April 23, 2022, the Biden administration pledged to cut greenhouse gas emissions by 50-52% by 2030. In addition, the EPA limited pollution allowed from vehicle tailpipes, adopted new standards for power plants, requiring coal plants to reduce 90% of their greenhouse gas pollution by 2039, and unveiled the Greenhouse Gas Reduction Fund.
The World Resources Institute tracked climate action under the Biden Administration here. If the Biden administration spent much of its time reinstating climate regulations dismantled by Trump, the second Trump administration focused on gutting them once again. The Columbia Law School’s Sabin Center for Climate Change Law has creating some detailed trackers: a Climate Deregulation Tracker for Trump’s first administration, a Climate Reregulation Tracker for the Biden administration, and a Climate Backtracker for Trump’s second administration.
Speaking at the UN in September 2025, President Trump declared climate change the “greatest con job ever perpetrated on the world,” and his second administration has been dedicated to gutting programs under the IRA, cutting federal funding for research, and erasing mentions of climate change from government websites, while advancing a fossil fuel energy agenda.
