The world has been around 1.5 °C warmer for over a year : Revista Pesquisa Fapesp

There is no question that the planet is getting hotter. Between January and March of 2016, the average temperature of the Earth’s atmosphere was at least 1.5 degrees Celsius (°C) above the standard reference value of the preindustrial era, when the first records of global temperatures on the Earth’s surface were collected in the second half of the nineteenth century. These data from eight years ago were the first from the European Union’s Copernicus Climate Change Service to signal an increase of this magnitude over a substantial time period. In the first two months of 2020, the 1.5 °C limit was surpassed once more.

The situation has become even worse since the middle of last year. Between July 2023 and June 2024, the average global warming value measured by the European service was equal to or greater than 1.5 °C every month. Only in July 2024 was the result slightly lower: with an increase of 1.48 °C. “The streak of record-breaking months has come to an end, but only by a whisker. Globally, July 2024 was almost as warm as July 2023, the hottest month on record. July 2024 saw the two hottest days on record,” said British climatologist Samantha Burgess, deputy director at Copernicus, in a press release. “The overall context hasn’t changed. Our climate continues to warm.”

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Data from other services that monitor global warming, such as the US National Oceanic and Atmospheric Administration (NOAA), indicate the same trend. For at least a year now, the world has been experiencing an extremely hot climate that is unprecedented in recent history. While a temperature increase of 1.5 °C—considered the most the world could withstand without suffering too many catastrophic consequences—is clearly undesirable, it is still within an acceptable margin of adaptation. However, it is possible that this perspective is too optimistic, given the droughts and floods that have devastated various regions of the planet in recent years, including in Brazil (where there have been droughts and wildfires in the Amazon and Pantanal, and storms in the far south).

In 2015, the Paris Agreement established a goal of limiting global warming in the following decades to a maximum of 2 °C, but preferably 1.5 °C, through drastic reductions in greenhouse gas emissions. Do the occurrences of extremely high temperatures mean that this goal has become unfeasible? It is not possible to say for sure. “The agreement does not specify in detail how the level of global warming is calculated,” says mathematician Thelma Krug, who was vice chair of the UN’s Intergovernmental Panel on Climate Change (IPCC) from 2015 to 2023. “Even if the 1.5 °C limit has already been exceeded on some occasions, this does not necessarily signify a long-term increase.” Most recent documents and studies cite that global warming has increased the global temperature by 1.2 °C over the preindustrial average. Krug states that the ideal approach would be for climate agreements to use an average from at least 10 years, maybe even 20, when calculating the level of global warming, which is similar to what the IPCC does.

Researchers at the Met Office Hadley Centre, the UK’s leading climate research center, published an opinion piece in the journal Nature in December 2023 in which they advocated for a similar approach. “It might come as a surprise that the Paris statement contains no formally agreed way of defining the present level of global warming. The pact does not even define ‘temperature increase’ explicitly and unambiguously. Without an agreed metric, there can be no consensus on when the 1.5 °C level has been reached,” they wrote.

The authors suggested a new index for calculating the level of global warming over a year. Their formula uses a combination of observational data from the last 10 years and climate model projections for the next 10 years. This way, it would not take such a long time to establish whether the 1.5 °C limit has been exceeded.

Significant variations in the average annual global temperature are common, just as thermal fluctuations can occur throughout a day or a month. They do not always reflect an underlying trend. This, however, does not appear to be the case with the temperature records that have been broken year after year for the past two decades.

The central question is whether this breach of the 1.5 ºC global warming limit is just part of Earth’s current weather or if it has established itself as the climate. Weather and climate use the same meteorological variables, such as humidity, pressure, and temperature, but over very different time periods. Weather is transient and reflects conditions in the short term—an hour, a day, even a week. It can change quickly. The climate is something more permanent, with some level of recurrence, and is typical of a given place. Its parameters usually reflect an average of weather records over a 30-year period. It therefore changes more slowly.

Climatologist Carlos Nobre, from the Institute of Advanced Studies at the University of São Paulo (USP), believes it is not yet possible to categorically state that global warming has reached 1.5 ºC. He argues that we need to wait another two years to see if global temperatures remain at the current high levels. “It is undeniable, however, that no climate models predicted that we would reach a level of global warming as quickly as we did,” points out Nobre. “This happened five to 10 years ahead of schedule.” According to the climatologist, there is no plausible scientific explanation for the rise in recent temperatures. “There has been a 0.2 °C increase in temperature that no one understands. We must be failing to identify some phenomenon that influences global warming,” Nobre says.

The story above was published with the title “1.5 °C warmer for a whole year” in issue 343 of September/2024.

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