Earth breached 2 degrees of warming for the first time. What does that mean?

Last week, global temperatures appeared to momentarily exceed a threshold set by governments around the world to try to avoid widespread climate devastation.

On November 17 and 18, the global temperature was on average 2 degrees Celsius warmer than pre-industrial levels for the first time in modern history.

The pre-industrial period was a time before the widespread use of fossil fuels.

The burning of fossil fuels released substances like carbon dioxide (CO2) into the atmosphere, trapping heat on the planet’s surface as part of the greenhouse effect.

Governments around the world agreed to the Paris Agreement in 2015 to keep average global warming well below 2°C, and ideally below 1.5°C.

Exceeding the 2°C threshold for a few days is not the end of the world, experts say, but it is just another sign of the extent of global warming.

And it comes as countries prepare to meet at the 28th United Nations Climate Change Conference (COP28) to discuss reducing fossil fuels.

A complex subject when coal production is expected to increase until 2030, and oil and gas production until 2050 and beyond.

How do we know we have passed the 2Cs?

This figure was calculated by the European Center for Medium-Range Weather Forecasts through one of its observation programs, the Copernicus Climate Change Service.

The service uses a model, called ERA5, which provides hourly estimates of atmospheric, land and ocean data from 1940 to the present.

The center arrived at the 2°C figure by comparing surface air temperatures from last week of ERA5 to those from 1850 to 1900.

Although international agreements refer to “pre-industrial” temperatures, there is no agreement on the exact period this covers.

But the UN’s Intergovernmental Panel on Climate Change (IPCC), which is the main body responsible for guiding international climate policy, used the period 1850-1900 as a benchmark for its reports.

Mark Howden, of the Australian National University and director of the Institute for Climate, Energy and Disaster Solutions, said the dataset was reliable and had a slight “cold bias”.

“But over the last few years they have all converged and so now there is very little difference.”

Joëlle Gergis, ANU climate lecturer and research associate at the ARC Center of Excellence for Climate Extremes, said scientific rigor relied on replicating results on other datasets.

“(ERA5) starts in 1940, so it only reports anomalies over a relatively short period of time,” Dr. Gergis said.

The result would be more meaningful, she added, if replicated by datasets stretching back to the 19th century.

What difference does a day make?

A day or two of above-average temperatures does not mean we have exceeded the Paris Agreement goals.

Dr Gergis said people should be careful not to overinterpret a single temperature anomaly over a day, week or even month.

“There is a lot of natural variability and random noise in all data sets,” she said.

“What is more important is the consistent long-term trend that is typically measured over 30-year reference periods.

“The Paris Agreement refers to sustained temperature anomalies of around 2°C, not just temperature deviations over a single day or month.”

So although the planet in the 1950s may have first reached a day when it was 1°C warmer than in pre-industrial times, it was not until 2017 that the IPCC declared that the Earth was on average 1°C warmer.

Currently, the planet is about 1.1°C warmer than in pre-industrial times.

Last year, the temperature was about 1.3°C warmer than before the widespread burning of fossil fuels began.

Changes from 1884 to 2022 in global temperatures from colder than average to warmer.(Provided: NASA Science Visualization Studio)

Katrin Meissner, director of the Climate Change Research Center at the University of New South Wales, warned there was nothing magical about a threshold of 1.5°C or 2° vs.

She said every tenth of a degree of warming would be dangerous.

“There is nothing ‘special’ about 2°C from a climate science perspective; the hotter it gets, the more dangerous it becomes,” Professor Meissner said.

“What we see in this report is what we have been predicting for years. Temperatures are increasing and there is also natural climate variability.

“With an El Niño phenomenon underway, I would expect temperatures to break records now and over the coming summer.”

2023 promises to be the hottest on record

A report The UN’s World Meteorological Organization said earlier this year that 2015 to 2022 were the eight warmest years on record, despite the cooling influence of a La Niña event in three of those years.

Earlier this month, he also noted that greenhouse gases have reached a record levelstating: “The last time Earth experienced a comparable concentration of CO2 was 3 to 5 million years ago, when the temperature was 2 to 3 degrees Celsius warmer and sea levels were 2 to 3 degrees Celsius warmer. 10 to 20 meters higher than today.

Professors Meissner, Howden and Gergis all said this year would likely be the hottest on record, surpassing the previous peak in 2016.

Ocean temperatures also reached new highs earlier this year.

Professor Meissner said warming must be reduced as soon as possible.

“The only way to do this is to stop emitting fossil fuels,” she said.

Professor Howden said the public should view the latest observations as signs that the global climate is changing, and that it is happening more quickly and more severely than expected.

“To avoid further changes, we must begin to quickly and significantly reduce greenhouse gas emissions,” he said.

The global community will meet next week

Countries will have the opportunity to try to reduce CO2 emissions at COP28, which begins next week.

The Dubai gathering will include the first “global stocktake,” which is a system for determining whether Paris Agreement countries are making progress in tackling climate change.

The results of the review could influence an acceleration of decarbonization for the next round of global climate action plans due in 2025.

Two studies published earlier this year showed that the world had already spent half of its remaining climate budget to keep warming below 1.5°C.

An estimation only six years left in the budget at the current rate of emissions.

Both studies also say the world must reach net zero emissions by 2035 to have a 50% chance of keeping warming below 1.5°C.

Australia plans to reach net zero emissions by 2050.