Consensus needed on when global warming will reach 1.5C, scientists say

Write in the journal Nature Ahead of COP28, a team of Met Office scientists highlighted that, surprisingly, there is currently no formally agreed way of defining the current level of global warming relevant to the Paris Agreement.

They proposed a solution.

Even if the global average temperature in a given year is well known, it will not be a suitable indicator of whether the Paris 1.5 target has been exceeded or not, as the Paris Agreement refers to the warming in the long term and not in individual years.

But no alternative has yet been formally agreed.

Without agreement on what would constitute a violation of Paris 1.5, there could be confusion and delay in responding.

Professor Richard Betts MBE, of the Met Office and University of Exeter, is lead author of the paper.

He said: “Clarity on breaching the safeguards of the Paris Agreement will be crucial.

“Without agreement on what will actually be considered above 1.5°C, we risk distraction and confusion at precisely the moment when it becomes even more urgent to act to avoid the worst effects of climate change.”

New indicators of global warming levels

Some of the currently proposed measurements rely on long-term averages – typically two decades – of global annual temperature.

Professor Betts added: “Using the average global temperature over the last 20 years would mean we would have to wait ten years to confirm whether the 1.5°C ceiling has been reached: creating a decade of otherwise avoidable delay.

“Today we recommend an indicator that combines the last ten years of global temperature observations with an estimate of the projection or forecast for the next ten years.

“If passed, it could mean a universally accepted measure of global warming that could trigger immediate action to prevent further increases.”

Using this suggested approach, the researchers found that the current level of global warming is around 1.26°C, with an uncertainty range of 1.13°C to 1.43°C.

It is more than likely that over the next five years, temperatures will reach or even exceed 1.5°C above pre-industrial levels.

But even an abnormally warm year would not mean we have reached the first safeguard of the Paris Agreement.

The Earth’s climate system exhibits a range of natural variability in which annual temperature fluctuates within small margins.

Professor Betts added: “Using an indicator of several years of observations and projections will smooth out natural variation to reveal underlying human-induced warming.”

Global temperature 2023

Provisional estimates of global average surface temperature for 2023 suggest the year could be the warmest on record.

The year is expected to exceed the level reached in 2016; currently the hottest year on record. 2023 is expected to continue the streak of warmest years on record since 1850.

Starting in 2015, the series includes years at both ends of natural climate variability.

Some years, such as 2016 and 2023, will have been naturally warmer due to the influence of El Niño, when a natural warming of parts of the tropical Pacific temporarily warms the planet by a small margin.

But the series also includes years that should have been naturally slightly cooler.

Professor Betts concluded: “The fact that the hottest years on record include both highs and lows in natural climate variability is further evidence that climate change driven by greenhouse gas emissions of human origin dominates recent climate records. »

Global Warming Dashboard

To complement the newly proposed indicators, a new section has been added to the Met Office climate dashboard to illustrate the current level of global warming.

The Global Warming Indicators dashboard displays eight separate indicators as well as the global average temperature observed using Met Office HadCRUT5 data.

The page also displays an indicator of current global warming for all eight methodologies, as well as a table explaining each indicator with a central estimate number and uncertainty limits.