The UN's 10,000-page red alert on climate change

Islie Bottollier-Depois.

There is only one way to avoid catastrophe and that is to drastically reduce greenhouse gas emissions.

These are the main conclusions from a trio of UN reports on climate change that were published in August, February and Monday. The three tomes focus on physical science, impacts and the need to adapt, and how to slash carbon pollution.

The Intergovernmental Panel on Climate Change delivered its first report in 1990 and positioned itself as the final word on the science behind global warming.

There are five key findings from the reports.

It is beyond a doubt.

Whatever climate sceptics say, scientific evidence shows that human activity is to blame for global warming, which has seen the planet heat up an average of 1.1 degrees Celsius above preindustrial levels.

The atmospheric concentration of CO 2 rose at least 10 times faster between 1900 and 2019 than any time in the last 800,000 years, and is at its highest in two million years.

Bye bye 1.5C?

If possible, the Paris Agreement calls for capping global warming at 2C and 1.5C. Most countries have embraced the more ambitious goal because of the deadly impacts already being felt and the new science.

The ship may have sailed.

Earth's average surface temperature will increase by 1.5C or 1.6C by around 2030, a decade earlier than the estimates made a few years ago.

In theory, it will be possible to cap temperature increases to below the 1.5C threshold by the end of the century, but even a temporary overshoot could cause irreversible damage to fragile ecosystems at the poles, in the mountains, and in coastal areas.

Staying under 2C will be a serious challenge if countries don't improve on emissions reduction pledges made under the Paris treaty. Current national policies would cause Earth to warm by 2200.

There was a lot of suffering.

Climate change has become a problem that is here and now. Between 3.3 and 3.6 billion people are vulnerable to global warming's deadly impacts, which are certain to get worse.

Extreme heat waves are so extreme that they are unliveable, superstorms made more deadly by a water-logged atmosphere and rising seas, and more disease-carrying mosquitoes and ticks.

These and other impacts are set to become worse, and will disproportionately ravage Earth's most vulnerable populations.

Hundreds of millions could eventually be forced from their homes by sea levels that will rise due to melting ice sheets on glaciers.

Even if global heating is capped at 2C, the oceans could gain half ametre by the year 2300.

Only one option left.

Decision makers can make the right choices to ensure a liveable future for the planet and its inhabitants, according to the IPCC.

All roads lead to a 1.5C or even a 2C world and in most cases immediate greenhouse gas emissions reductions in all sectors.

It will take a massive reduction in fossil fuel use to hit the temperature goals.

Within eight years, the use of coal plants that don't deploy carbon capture must decline by 70 to 90 percent.

There are tipping points.

The new trio of reports from the Intergovernmental Panel on Climate Change emphasize the danger of tipping points in the climate system that could result in catastrophic and irreversible change.

The good news is that we seem to have pulled back from emissions scenarios that could result in a 4C or 5C world. The good news is that there are low probability and high impact tipping point scenarios in nature.

The Amazon basin could be transformed into a savanna if the melting of the ice sheets that hold the greenhouse gases that cause global warming is not stopped.

Where are the triggering events? The risk is higher in a world that has warmed 2C above 19th century levels than it is in a world that has warmed 1.5C.

The risk is very high above 2.5C.

There will be a new year in 2022.

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