Is it too late to reverse climate change?

Is it too late to reverse climate change? I'll gather the latest science on what can still be turned back.

No — but it depends what you mean by "reverse."

Scientists make a clear distinction between limiting future warming and undoing warming and impacts that have already happened.

1. Some climate change is already irreversible on human timescales

> "A large fraction of climate change is largely irreversible on human time scales," the most recent assessment report from the Intergovernmental Panel on Climate Change (IPCC) warned.

According to NASA and the IPCC:

> modern humans have never before seen the observed changes in our global climate, and some of these changes are irreversible over the next hundreds to thousands of years.

A study of reversibility concluded:

> climate change cannot be completely reversed even if all the external forces are returned to their initial values.

That is because of built-in inertia in the system:

Other impacts are effectively permanent:

> A later decline in global temperature does not reverse all damage.

Research on overshoot — where temperatures temporarily exceed 1.5°C and then come back down — found that damages such as rising sea levels cannot be reversed.

The IPCC and UN Environment Programme also warn of tipping points with irreversible and cascading effects, including:

> the loss of the West Antarctic and Greenland ice sheets, the loss of the Amazon rain forest and the shutdown of the Atlantic Ocean circulation system that keeps much of Europe warm.

Scientists note that if we stay over 1.5°C, we risk triggering climate tipping points — sudden shifts that cannot be undone on human time scales.

2. It is not too late to prevent the worst impacts

The widespread notion that the climate is something we can fix later is a misconception. In fact:

> The severity of effects caused by climate change will depend on the path of future human activities... if we can reduce emissions, we may avoid some of the worst effects.

NASA notes:

> Humans have caused major climate changes to happen already, and we have set in motion more changes still. However, if we stopped emitting greenhouse gases today, the rise in global temperatures would begin to flatten within a few years. Temperatures would then plateau but remain well-elevated for many, many centuries.

The IPCC's message in its 2023 Synthesis Report was summarized as:

> "It is still possible to halt current climate change trends and secure a liveable future for all, according to the new IPCC report. But the window of opportunity is narrowing quickly; we must act now".

Other summaries of the IPCC put it simply:

> It is not too late to make a difference, but it requires an unprecedented level of cooperation, innovation, and determination

and

> It will never be too late to take action for the climate.

3. What "reversal" would actually require

Completely reversing climate change overnight is not possible. However, we can significantly reduce its impacts by lowering greenhouse gas emissions and restoring natural ecosystems.

The IPCC said:

> Only if human emissions were "strongly negative over a sustained period"—for example, if tree planting and other activities were to sequester far more carbon than humans release—would climate change begin to be reversed.

Other research suggests:

> partial reversal is theoretically possible through aggressive emission reductions combined with massive carbon dioxide removal efforts.

Studies also show that tipping risks from overshooting 1.5°C can be minimised if warming is swiftly reversed.

That is, we cannot go back to the climate of 1850, but every tenth of a degree of avoided warming matters. Rapid cuts to CO2, methane and other greenhouse gases, plus removing CO2 from the atmosphere, can flatten the temperature curve and limit how long we stay above 1.5°C and the extent of irreversible damage.

Bottom line: It is too late to completely reverse climate change to its pre-industrial state without centuries of sustained negative emissions, and some changes like sea-level rise and ice-sheet loss are locked in for hundreds to thousands of years. It is not too late to halt further warming, avoid triggering more tipping points, and prevent a much worse future — but the window to do so is narrowing quickly.