Is it too late to reverse climate change?

Is it too late? I'll pull the latest science on what climate change can still be reversed.

No, it is not too late to act on climate change, but it is too late to completely reverse it to pre-industrial conditions on a human timescale without sustained negative emissions.

1. Some change is already 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, every little bit of avoided future temperature increases results in less warming

The most recent assessment from the Intergovernmental Panel on Climate Change (IPCC) warned:

> “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.

This is because:

And over several thousand years, Earth would dial temperatures back down to preindustrial levels via natural carbon sinks, such as trees and soils absorbing CO2, according to NOAA.

Even if Earth's climate was stabilized soon, some climate change-induced damage could not be reversed within centuries or even millennia. Other assessments note:

> While some of the changes will be irreversible for millennia, some can be slowed and others reversed through strong, rapid and sustained reductions in greenhouse gas emissions.

2. Tipping points - irreversible but with a small window

Tipping points are defined as:

> critical thresholds in a system that, when exceeded, can lead to a significant change in the state of the system, often with an understanding that the change is irreversible.

Examples include collapse of the Greenland and West Antarctic ice sheets, dieback of the Amazon rainforest, shutdown of the Atlantic Meridional Overturning Circulation (AMOC), and thawing permafrost releasing methane.

Historically, crossing these thresholds has been assumed to be a point of no return, but a study published in Nature found:

> they could be ‘temporarily exceeded’ without prompting permanent environmental changes.

Researchers said:

> The disastrous consequences of climate 'tipping points’ could be averted if global warming is reversed quickly enough

However the time available depends on the level of warming:

> The more extreme the warming, the less time we would have to prevent tipping points.
> This is especially true for fast-onset tipping points like Amazon forest dieback and disruption to monsoons, where irreversible change could take place in a matter of decades.
> Slow-onset tipping points take place over a timescale of many centuries and – depending on the level of warming – this would give us more time to act.

3. It is not too late to limit the worst impacts

Scientists phrase the answer this way:

> Global average temperatures have risen and weather extremes have already seen an uptick, so the short answer to whether it's too late to stop climate change is: yes. But there's still time to prevent cascading effects, as every degree of additional warming has exponentially disastrous impacts, experts say.

NOAA puts it simply:

> 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.

Although scientists estimated it's still possible to stay within these limits, they said it would require immediate, rapid and large-scale reductions in greenhouse gas emissions.

Without major action, current estimates show:

> 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.

Once 1.5°C is reached, there will be increasing heat waves, longer warm seasons and shorter cold seasons. When 2°C is crossed, critical tolerance levels for agriculture and health will be reached.

4. What would reversing or slowing require?

According to NASA and IPCC, response requires two tiers:

> - “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.

To actually reverse warming, not just slow it, humanity would need to reach net-zero and then net-negative emissions:

> A further increase of [carbon dioxide removal], until a situation with net zero or even net-negative GHG emissions is reached, would increase the pace at which historical human-induced warming is reversed after its peak

Experts say:

> 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 and soot (“black carbon”).

Transitioning to solar, wind, biofuels, and nuclear can slow the pace, though these energy sources face hurdles ranging from manufacturing capacity to debates about where to install facilities.

Geoengineering proposals like injecting reflective particles into the stratosphere or seeding oceans with iron could work in principle, but many climate scientists oppose undertaking geoengineering until we have a much better understanding of possible side effects.

Bottom line: