The short answer: very little, and it depends on what you mean by “stop.” The carbon budget for limiting warming to 1.5°C above preindustrial levels, the target set by the Paris Agreement, stands at roughly 170 billion tonnes of CO2. At current emission rates, that budget runs out before 2030. The world isn’t out of time entirely, but every year of delay locks in more severe consequences that last centuries.
The 1.5°C Budget Is Nearly Gone
Think of the atmosphere as a bathtub. The total amount of CO2 humanity can ever emit while keeping warming below a certain threshold is the “carbon budget,” and for 1.5°C, the tub is almost full. The remaining budget of 170 billion tonnes of CO2 sounds enormous, but global fossil fuel emissions hit a record high of 37.8 billion tonnes in 2024 alone. At that pace, the entire 1.5°C budget disappears in roughly four years.
The IPCC laid out what staying under 1.5°C would have required: global greenhouse gas emissions peaking before 2025 and falling 43% by 2030, with methane emissions dropping by about a third over the same period. For the less ambitious target of 2°C, emissions still needed to peak before 2025 and drop by 25% by 2030. Emissions have not peaked. They rose 0.8% in 2024.
This doesn’t mean 1.5°C is guaranteed to be breached permanently in four years. Carbon budgets estimate cumulative emissions over time, and the relationship between emissions and temperature involves some uncertainty. But the World Meteorological Organization puts the likelihood that at least one year between 2024 and 2028 will temporarily exceed 1.5°C at 80%. A temporary spike is different from a sustained breach, yet the trend line is clear: the window for 1.5°C is closing in years, not decades.
What Happens If We Miss 1.5°C
Missing 1.5°C doesn’t mean the fight is over. It means the consequences get measurably worse, and every fraction of a degree matters. The difference between 1.5°C and 2°C of warming looks small on paper but translates into real harm. At 2°C, 18% of insect species, 16% of plant species, and 8% of vertebrate species are projected to lose more than half their geographic range. At 1.5°C, those losses shrink by roughly half to two-thirds.
Sea level rise at 1.5°C is projected at about 0.4 meters (1.3 feet) by 2100, compared to 0.46 meters (1.5 feet) at 2°C. That extra six centimeters exposes an additional 10 million people to coastal flooding. These numbers assume no additional adaptation measures and current population levels, so they represent the baseline risk rather than a guaranteed outcome.
The deeper concern is tipping points: thresholds beyond which certain changes become self-reinforcing and effectively irreversible on human timescales. The slow collapse of the Greenland ice sheet, which holds enough ice to raise global sea levels by about 24 feet, is one of the most likely tipping elements in a world warmer than 1.5°C. Some models place the critical threshold at 1.6°C. More recent simulations estimate it could be as high as 2.7°C. That range of uncertainty is itself a reason to stay as far below these thresholds as possible.
How Fast the Planet Is Warming Now
The Earth has warmed about 2°F (1.1°C) since 1850. But the rate of warming has accelerated sharply. Since 1982, the planet has been warming at 0.2°C per decade, more than three times the long-term average of 0.06°C per decade. At the current rate, every five years adds roughly another tenth of a degree.
Even if all CO2 emissions stopped tomorrow, temperatures wouldn’t drop back to preindustrial levels anytime soon. Most climate models show that global temperatures stop rising within a couple of decades after emissions cease, but they remain elevated for centuries. The CO2 already in the atmosphere continues trapping heat long after it’s released. Stopping climate change, in the sense of returning to some earlier normal, is not something any living generation will see. The realistic goal is stopping it from getting worse.
Why Methane Cuts Buy Time Fastest
CO2 gets most of the attention because it’s the largest contributor to warming and persists in the atmosphere for centuries. But methane offers the fastest lever for slowing warming in the near term. Methane is about 200 times less abundant than CO2 in the atmosphere, and it breaks down within about a decade. But while it’s present, it traps far more heat: roughly 80 times as much as CO2 over a 20-year period.
That means cutting methane emissions today has a disproportionately large cooling effect within the next 10 to 20 years, precisely the window when the 1.5°C and 2°C thresholds are most at risk. Reducing methane doesn’t solve the long-term CO2 problem, but it can shave off some of the peak warming that triggers tipping points. Sources like natural gas infrastructure, livestock operations, and landfills are the main targets. The IPCC’s call for a one-third reduction in methane by 2030 reflects this urgency.
Where Global Commitments Actually Stand
Countries representing about 70% of global CO2 emissions have pledged to reach net zero, most by 2050. On paper, that sounds promising. In practice, the IEA has found that even if every current pledge were fully met, the world would still be emitting around 22 billion tonnes of CO2 in 2050. That’s far more than zero, and far more than the atmosphere can absorb without continued warming.
The gap between pledges and action is wide. Global emissions are still rising year over year, and the infrastructure being built today, power plants, factories, transportation networks, will operate for decades. Each new fossil fuel project extends the timeline for reaching net zero. The IEA has been blunt: commitments made to date fall far short of what their net-zero pathway requires.
What the Timeline Actually Looks Like
There is no single deadline after which “it’s too late.” Climate change operates on a sliding scale. The question isn’t whether we can stop it, but how much warming we’re willing to accept and how quickly we act to limit it. Here’s what the timeline looks like in practical terms:
- Before 2030: The remaining carbon budget for 1.5°C is exhausted at current rates. Emissions need to fall roughly 43% from recent levels to preserve any chance at this target. Methane reductions in this window have the biggest short-term impact.
- 2030 to 2050: The difference between aggressive action and moderate action determines whether the world lands closer to 1.5°C or overshoots 2°C. Net-zero commitments need to translate into actual emission reductions during this period, not just pledges.
- 2050 and beyond: Even under optimistic scenarios, some warming is locked in. The focus shifts to whether tipping points have been avoided and whether temperatures stabilize or continue climbing.
The framing of “how much time do we have” can be misleading because it implies a binary: either we make it or we don’t. In reality, every tonne of CO2 that stays unburned makes the future slightly less dangerous. Every year emissions keep rising makes the required cuts steeper and the locked-in consequences worse. The physics doesn’t care about deadlines. It responds to cumulative emissions, and right now, that total keeps growing at record speed.