Climate change is caused by the buildup of heat-trapping gases in Earth’s atmosphere, primarily from burning fossil fuels. Since the start of the Industrial Age, the concentration of carbon dioxide in the atmosphere has increased 50 percent, from about 280 parts per million to nearly 423 ppm in 2024. That surge has pushed the global average surface temperature up by 1.35°C (2.62°F) above pre-industrial levels, making 2024 the warmest year since records began in 1850.
How Greenhouse Gases Trap Heat
Earth’s atmosphere naturally contains gases that act like a blanket around the planet. Sunlight passes through the atmosphere and warms the surface, which then radiates heat back upward. Greenhouse gases absorb some of that outgoing heat and redirect it back toward the surface, keeping the planet warmer than it would otherwise be. Without any greenhouse effect at all, Earth would be a frozen, uninhabitable world.
The problem is scale. When humans add enormous quantities of carbon dioxide, methane, and other gases to the atmosphere, the blanket gets thicker. More heat gets trapped, less escapes to space, and the planet’s temperature rises. Carbon dioxide is the biggest contributor simply because we release so much of it, but other gases pack a heavier punch molecule for molecule. Methane traps 27 to 30 times more heat than carbon dioxide over a 100-year period. Nitrous oxide is 273 times more potent than carbon dioxide over the same timeframe.
Where the Emissions Come From
Energy production is the dominant source, responsible for nearly three-quarters of global greenhouse gas emissions. Within that sector, electricity and heat generation lead the way, followed by transportation and manufacturing. Every time a coal plant generates power, a car burns gasoline, or a factory runs on natural gas, carbon dioxide enters the atmosphere.
Agriculture is the second-largest contributor. Livestock produce methane during digestion, rice paddies release it from flooded soils, and synthetic fertilizers break down into nitrous oxide. These agricultural emissions are harder to eliminate than energy emissions because they’re tied to biological processes rather than fuel choices.
Some industrial processes release carbon dioxide through chemistry alone, independent of fuel burning. Cement production is a major example. Making the calcium-based compound at the heart of cement requires heating limestone to extreme temperatures, which chemically breaks it down and releases carbon dioxide as a byproduct. The cement industry accounts for 7 to 8 percent of all human-caused carbon dioxide emissions globally.
Deforestation Removes a Natural Buffer
Forests pull carbon dioxide out of the air and store it in wood, roots, and soil. When those forests are cut down or burned, that stored carbon goes back into the atmosphere. Tropical deforestation alone released an estimated 0.8 to 2.2 billion metric tons of carbon per year during the 1990s. Rates have slowed since then, dropping to roughly 1 billion metric tons per year during 2010 to 2019, but the damage compounds over time.
Deforestation also reduces the planet’s future capacity to absorb emissions. Every hectare of forest cleared is one less hectare pulling carbon out of the air. Research published in Nature Communications found that deforestation doesn’t just release carbon directly; it also reduces the carbon storage ability of the tropical forests that remain, creating a cascading effect.
Why Natural Cycles Don’t Explain It
Earth’s climate has always changed. Slow shifts in the planet’s orbit around the sun, known as Milankovitch cycles, have driven ice ages and warm periods over tens of thousands to hundreds of thousands of years. But these cycles operate far too slowly to explain what’s happening now. Over the last 150 years, orbital changes have barely altered the amount of solar energy Earth absorbs. NASA satellite measurements show solar radiation has actually decreased slightly over the past 40 years.
The contrast is stark. Since 1750, the warming driven by greenhouse gases from fossil fuels is over 50 times greater than any additional warming from the sun itself. Climate models show that once atmospheric carbon dioxide exceeds about 350 ppm, its warming effect overwhelms any influence from orbital cycles. We passed that threshold decades ago and now sit above 420 ppm. Without human influence, Earth’s current orbital position would predict a cooling trend, continuing a gradual decline that began 6,000 years ago. Instead, the planet is warming rapidly.
The Ocean Is Absorbing Most of the Heat
The air temperature increase of about 1.35°C only tells part of the story. More than 90 percent of the excess heat trapped by greenhouse gases has been absorbed by the oceans. This is an enormous amount of energy. It drives ocean warming from the surface down to significant depths, fuels stronger hurricanes, accelerates the melting of ice shelves from below, and causes seawater to expand, contributing to sea level rise.
Ocean heat absorption has temporarily slowed the warming of the atmosphere, essentially buying time. But that heat doesn’t disappear. It continues to circulate through ocean currents and will influence climate patterns for centuries, even if emissions dropped to zero tomorrow.
Feedback Loops That Accelerate Warming
Once warming begins, several natural processes amplify it. The most powerful is the ice-albedo feedback. Sea ice and snow are white, reflecting 50 to 70 percent of incoming sunlight back into space. The open ocean, by contrast, reflects only about 6 percent and absorbs the rest. As warming melts ice, it exposes darker ocean water underneath, which absorbs more heat, which melts more ice, which exposes more dark water. The cycle feeds itself.
This feedback is already visible in the Arctic, where sea ice extent has declined sharply over recent decades. Earth’s overall albedo (its reflectivity, measured at 0.30) directly influences the planet’s energy balance. As ice loss shifts that number downward, even slightly, more solar energy stays in the system and global temperatures rise further.
Other feedbacks compound the problem. Warming thaws permafrost in Arctic and subarctic regions, releasing methane and carbon dioxide that have been locked in frozen soil for thousands of years. Warmer air holds more water vapor, which is itself a greenhouse gas, trapping additional heat. Each of these loops means that the warming caused by fossil fuel emissions triggers additional warming on top of it, making the climate more sensitive to every ton of carbon dioxide we add.