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 saved and what can't be undone.

Short answer: No, it is not too late to limit the worst of climate change, but it is too late to completely reverse it quickly - and some changes are already irreversible on human timescales.

Here is what the science says:

1. Some warming and impacts are already locked in

> Humans have caused major climate changes to happen already, and we have set in motion more changes still.

NASA explains that even if we stopped emitting greenhouse gases today, the rise in global temperatures would begin to flatten within a few years, but temperatures would then plateau but remain well-elevated for many, many centuries.

There is a time lag between what we do and when we feel it, but that lag is less than a decade.

The IPCC warns that:

> A large fraction of climate change is largely irreversible on human time scales

And:

> 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.

Research on reversibility also finds:

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

Completely reversing climate change overnight is not possible.

2. It is NOT too late to avoid the worst - every fraction of a degree matters

> While the effects of human activities on Earth's climate to date are irreversible on the timescale of humans alive today, every little bit of avoided future temperature increases results in less warming that would otherwise persist for essentially forever.

> The benefits of reduced greenhouse gas emissions occur on the same timescale as the political decisions that lead to those reductions.

NASA states:

> But it may not be too late to avoid or limit some of the worst effects of climate change.

The IPCC and other assessments echo this:

> While some effects of climate change are irreversible, it is not too late to act. The IPCC states that urgent and immediate action is needed to avoid the worst impacts.

> The short answer is that it's not too late to act, but our past actions may have already locked in certain outcomes and action is needed to avoid more substantial impacts in the future.

There is no single planetary tipping point where all hope is lost:

> While these benchmarks can be important for understanding the fragility of specific species and ecosystems, the IPCC confirms that there is no "tipping point" for the planet as a whole

> every bit of warming we avoid will reduce the extremes of climate fluctuation. ... It will never be too late to take action for the climate.

Without major action, however:

> Without major action to reduce emissions, global temperature is on track to rise by 2.5°C to 4.5°C (4.5°F to 8°F) by 2100, according to the latest estimates.

3. Why "reversal" is so hard - tipping points

Some Earth systems have tipping points where change becomes self-reinforcing and irreversible for centuries to millennia, even if warming stops later.

Research shows that:

> multiple climate tipping points could be activated as the Earth progresses past 1.5°C of global warming for an extended period, resulting in irreversible and potentially catastrophic climate disruptions.

Examples include loss of the West Antarctic and Greenland ice sheets, loss of the Amazon rain forest and shutdown of Atlantic Ocean circulation.

Irreversibility is key:

> Although some tipping points may be theoretically reversible over thousands or millions of years, they are effectively permanent within investment- and policy-relevant timeframes. For example, the collapse of the Greenland Ice Sheet, once past a critical threshold, could take millennia to replace even if global temperatures drop.

Once a process passes a tipping point it will keep on going even if you remove the initial driver.

4. Can climate change actually be reversed in the future?

Only with sustained negative emissions - removing more CO2 than we emit for decades.

> 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.

And:

> we can significantly reduce its impacts by lowering greenhouse gas emissions and restoring natural ecosystems.

Once we reach net zero, warming slows dramatically:

> Once global net zero is achieved, further global warming is expected to significantly slow down, but the effects of existing atmospheric greenhouse gases will still contribute to continued warming.

The IPCC timelines for that are tight:

> The IPCC has stated that limiting warming to 2°C requires reaching net-zero carbon dioxide emissions globally by the early 2070s. For 1.5°C, that deadline was the early 2050s, a target that is slipping out of reach.

That will require both:

Mitigation includes rapid decarbonization of energy, transport, industry, stopping deforestation, and enhancing carbon sinks through forests, soil carbon, direct air capture and other carbon dioxide removal technologies. Adaptation includes building resilience to sea-level rise, heat waves, drought, wildfires and stronger hurricanes that are already projected to continue through this century and beyond.

Bottom line

In NASA's phrasing: it's not too late to act, but the key question is, what will our emissions of carbon dioxide and other pollutants be in the years to come.