The single most significant cause of long-lasting climate change is the buildup of carbon dioxide in Earth’s atmosphere. Unlike weather patterns that shift over days or seasons, CO2 persists for centuries once released, trapping heat and warming the planet on timescales that stretch far beyond a human lifetime. As of May 2025, atmospheric CO2 has reached 430 ppm, a level not seen in millions of years and one that continues to climb.
Why CO2 Causes Change That Lasts Centuries
Carbon dioxide is not the most potent greenhouse gas molecule for molecule, but it is the most consequential for long-term climate shifts because of how long it stays in the atmosphere. Individual carbon atoms cycle through the atmosphere on a timescale of roughly 5 to 25 years, moving between air, ocean, and land. But when you add a large pulse of extra CO2, the portion that remains after those quick exchanges sticks around for centuries. There is no fast natural process to pull it all back out.
This persistence is what separates CO2 from a gas like methane. Methane is far more powerful in the short term, with roughly 80 times the heat-trapping ability of CO2 over a 20-year window. Over 100 years, though, that figure drops to about 27 to 30 times, because methane breaks down in the atmosphere within about a decade. CO2 does not. The warming it produces compounds year after year, decade after decade.
How CO2 Actually Traps Heat
Earth’s surface, warmed by the sun, radiates energy back toward space as infrared radiation. CO2 molecules absorb this outgoing infrared energy at specific wavelengths, particularly around 15 micrometers, and re-emit it in all directions, including back toward the ground. This is the greenhouse effect, and without any of it, Earth’s average surface temperature would be about minus 18°C (0°F) instead of the roughly 15°C (59°F) we experience. The natural greenhouse effect accounts for about 33°C of warming.
The problem is not that this process exists. It is that humans have increased the concentration of CO2 so dramatically that more infrared energy is being trapped than the climate system can balance. The result is a sustained energy imbalance: more heat coming in than going out.
Ice Cores Show CO2 and Temperature Move Together
Scientists have drilled deep into Antarctic ice sheets and extracted cores that contain tiny bubbles of ancient atmosphere, creating a record stretching back 800,000 years. Over that span, CO2 levels and Antarctic temperatures track each other with remarkable consistency, showing a statistical correlation of about 0.82 out of 1.0. Temperature swings of up to 12°C separate the coldest glacial periods from the warmest interglacials, and CO2 rises and falls in step.
During ice ages, CO2 hovered around 180 ppm. During warm interglacial periods, it reached about 280 ppm. Today’s level of 430 ppm is more than 50% higher than anything in that 800,000-year record, and the 3.5 ppm increase measured between May 2024 and May 2025 alone represents an astonishingly fast rate of change by geological standards.
Earth’s Orbital Shifts: The Natural Long-Term Driver
Before humans began burning fossil fuels, the primary driver of long-lasting climate change was slow, predictable shifts in Earth’s orbit around the sun. These are known as Milankovitch cycles, and they operate on three overlapping timescales.
- Eccentricity: The shape of Earth’s orbit stretches from more circular to more elliptical and back over a cycle of about 100,000 years. A more elliptical orbit means greater variation in the distance between Earth and the sun throughout the year.
- Obliquity: The tilt of Earth’s axis shifts between about 22.1 and 24.5 degrees over roughly 41,000 years. Greater tilt means more extreme seasons. The current tilt is 23.4 degrees and slowly decreasing.
- Precession: Earth wobbles on its axis like a spinning top, completing a full wobble roughly every 23,000 years. This changes which hemisphere is tilted toward the sun during the closest orbital approach.
These cycles don’t change the total amount of solar energy Earth receives very much. Instead, they redistribute it across seasons and hemispheres, which can trigger or end ice ages by affecting how much summer sunlight hits the northern continents. When summers are too cool to melt winter snow, ice sheets grow. When summers warm, they retreat. Crucially, these orbital shifts also triggered CO2 release from warming oceans, which then amplified the warming further. Even in the natural system, CO2 was the mechanism that turned a small orbital nudge into a global temperature shift.
Feedback Loops That Extend the Warming
One reason CO2-driven climate change is so long-lasting is that it triggers self-reinforcing cycles. The most concerning involves permafrost, the frozen ground covering vast stretches of the Arctic. Permafrost contains approximately twice the amount of carbon currently in Earth’s entire atmosphere, locked in frozen organic material that accumulated over tens of thousands of years.
As global temperatures rise, this ground thaws and microbes begin decomposing the ancient organic matter, releasing CO2 and methane. Estimates of how much carbon permafrost could release by 2100 range widely depending on how aggressively fossil fuel emissions are cut. Under strong climate policies, projections range from about 22 to 432 gigatons of CO2. Under weak policies, that figure could reach 550 gigatons. Wildfires in permafrost regions could increase these emissions by another 30 to 40%. Each release adds more greenhouse gas, which drives more warming, which thaws more permafrost.
The Ocean’s Shrinking Ability to Help
Oceans have historically absorbed a large share of the CO2 humans emit. Over the industrial era as a whole, the ocean has taken up about 48% of fossil fuel CO2 emissions. But this buffering capacity is weakening. Over the most recent decades measured, the ocean’s share of uptake dropped from roughly 44% to about 36%.
The reason is chemistry. As seawater absorbs CO2, it becomes more acidic, which makes it progressively harder for the water to absorb more. The surface ocean today is measurably less efficient at soaking up CO2 than it was before industrialization. This creates another positive feedback: as the ocean takes up less, more CO2 stays in the atmosphere, accelerating warming. The ocean does not stop absorbing CO2, but its role as a climate safety valve is gradually diminishing at the same time emissions continue to grow.
Why “Long-Lasting” Means Thousands of Years
The combination of CO2’s atmospheric persistence, self-reinforcing feedback loops, and the ocean’s declining absorption capacity means that climate change driven by CO2 operates on timescales most people find hard to grasp. Even if all emissions stopped tomorrow, the CO2 already in the atmosphere would continue warming the planet for centuries. The deep ocean takes roughly a thousand years to fully circulate, meaning the heat already absorbed will continue influencing surface temperatures long after concentrations stabilize.
Natural orbital cycles can drive climate shifts over tens of thousands of years. The current CO2-driven warming is producing a comparable magnitude of change in just a few centuries, and the effects will persist for a similarly long stretch. The carbon humans have added to the atmosphere is, for all practical purposes, a permanent alteration to the climate system on any timescale relevant to civilization.