By Mark Lynas

It’s the last chance for the climate. Of course, this is said before every annual Conference of Parties (COP) but for COP26, which starts this weekend in Glasgow, it really is the case.

Scientists are clear that to meet the 1.5-degree goal set by the Paris Agreement, global emissions of carbon need to be cut by half by the end of this decade. That won’t happen if COP26 fails, momentum is lost and climate targets are watered down.

The science of climate change is clearer than it has ever been. As we published recently in the peer-reviewed journal Environmental Research Letters, the consensus about the human-caused nature of the climate crisis is now at 99.9 percent, showing virtual unanimity in the expert community that global warming is caused by greenhouse gas emissions.

In other words, there is no longer anywhere for the skeptics to hide. The science is also clear that the budget for 1.5 degrees is rapidly running out, and that the existing NDCs (nationally-determined contributions, COP-code for the Paris pledges made by nations) do not collectively even restrain the planet’s warming to 2 degrees. Instead, we are on course for 2.7 degrees according to the latest analysis.

Youth rally in Milano, Italy, during pre-COP event on Oct. 1. Photo: Shutterstock/MAURO UJETTO

It is worth pausing for a minute to review the science behind these different temperature rise implications. A lot of people are beginning to say that it is time to admit that the 1.5-degree goal set in Paris is now out of reach, and that we should instead be focusing on two degrees. They are right, of course, that achieving 1.5 would involve a heroic effort.

But giving up on it would entail some pretty catastrophic impacts from climate warming. We don’t have to guess at what these might be; the Intergovernmental Panel on Climate Change (IPCC) wrote an entire report on 1.5 degrees.

Abandoning the target would result in a much faster rate of sea-level rise, which would permanently displace an additional 10 million people and put 136 coastal megacities at increased risk of flooding. The long-term viability of small-island nations like the Maldives would be jeopardized, which is why the foremost advocates of the 1.5-degree goal are the most vulnerable nations of the Climate Vulnerable Forum.

At 2 degrees, as compared to 1.5, an additional 1.7 billion people would be exposed to severe heatwaves, 420 million to extreme heatwaves and 65 million more to deadly heat. World food supplies would be endangered, with net reductions projected for staple crops like maize, rice and wheat due to extreme heat and drought unless radical adaptation measures are taken.

Abandoning 1.5 means abandoning hope for the world’s coral reefs, which would be rendered virtually extinct by the time planetary warming hits 2 degrees.

What if we miss even the 2-degree fallback Paris goal, as looks likely with current NDC pledges? This amount of heating would make the planet hotter than at any time since the Pliocene, 3-5 million years ago, when sea levels were 20 meters (65 feet) higher and there was no ice in the Arctic.

Climate models suggest that as warming approaches 3 degrees above pre-industrial temperatures, large parts of the tropics and sub-tropics — particularly focused around the Middle East, South and East Asia and southern China — would become biologically uninhabitable by humans for an extended part of the year.

Impacts on global biodiversity would be immeasurable, with the probable collapse of the Amazon rainforest ecosystem and subsequent release of vast amounts of additional carbon from that area and from melting permafrost in the Arctic.

One half of all insects, a quarter of all mammals, 44 percent of plants and a fifth of all bird species will lose more than half their climatic range by the end of the century with a global temperature rise of 3 degrees. This represents a mass extinction of geological significance.

That is why COP26 matters. It is easy to get lost in the detail of carbon market modalities, buzz-phrases like “loss and damage” and the endless fight over financing for mitigation and adaptation. All of these things are important components of a successful COP26 outcome, but it is critical to keep an eye on the bigger prize: significant increases in ambition that would put the planet back on the path to 1.5.

The Alliance for Science will be attending COP26 and will report back on progress. Watch this space — and make your voice count.