Is it too late to reverse climate change?

Is it too late to reverse climate change? I'll gather the latest science on what's still reversible — and what's not.

No, it is not too late to limit climate change - but fully reversing it to pre-industrial conditions is not possible on human timescales.

Science distinguishes between reversing past warming and preventing future warming:

1. Some changes are already locked in and largely irreversible

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

> While the effects of human activities on Earth's climate to date are irreversible on the timescale of humans alive today

The Intergovernmental Panel on Climate Change (IPCC) warns:

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

> 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.

Reasons for this inertia:

Some impacts are irreversible even at low warming:

> Additional warming above 1.5C "will result in irreversible impacts" on ecosystems such as coral reefs, mountain glaciers and ice sheets

> even warming of 1.5 degrees –a target that we will surely exceed at current rates of emissions– will unavoidably result in sea level rise of at least 2m over the next 2000 years, and 6m over the much longer term

And:

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

Tipping points make this more serious. The IPCC uses the term to refer to “critical threshold[s] beyond which a system reorganises, often abruptly and/or irreversibly.”

Past human activities have committed us to future changes scientists call our climate change "commitment".

Without major action, global temperature is on track to rise by 2.5°C to 4.5°C by 2100.

2. It is NOT too late to slow, limit, and eventually stabilize warming

> Yes. While we cannot stop global warming overnight, we can slow the rate and limit the amount of global warming by reducing human emissions of heat-trapping gases

> if we stopped emitting greenhouse gases today, the rise in global temperatures would begin to flatten within a few years

> every little bit of avoided future temperature increases results in less warming that would otherwise persist for essentially forever.

NASA's summary of the IPCC finding is:

> 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.

> “strong and sustained” reductions of greenhouse gases could lead to temperature stabilization in 20-30 years

NOAA makes the same point about thresholds:

> without dramatic action in the next couple of decades, we are unlikely to keep global warming in this century below 1.5° Celsius... —a threshold that experts say offers a lower risk of serious negative impacts. But the more we overshoot that threshold, the more serious and widespread the negative impacts will be, which means that it is never “too late” to take action.

With no further human influence, natural processes would begin to slowly remove excess CO2 and global temperatures would gradually begin to decline, but this is a slow process over centuries, not years.

3. What "not too late" actually means

Scientists frame the response as two parallel strategies:

> Responding to climate change will involve a two-tier approach: - "Mitigation" – reducing the flow of greenhouse gases into the atmosphere - "Adaptation" – learning to live with, and adapt to, the climate change that has already been set in motion.

Mitigation to avoid worse warming requires a major departure from business as usual in how the world uses and produces energy, including transition to solar, wind, biofuels, nuclear and other non-emitting sources.

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

Geoengineering proposals like injecting reflective particles or ocean iron fertilization could work in principle, but many climate scientists oppose undertaking them until we have a much better understanding of side effects, and the American Meteorological Society concluded research to date has not determined whether there are large-scale approaches that would produce significant benefits or whether those benefits would substantially outweigh detriments.

Bottom line:

It will never be too late to take action — every action matters to limit how bad it gets.