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July was the hottest month in recent history and broke temperature records

Global warming shows no signs of letting up, causing forest fires in the Northern Hemisphere’s summer and a mild winter below the Equator

In early August, wildfires brought fire, destruction, and death to the Hawaiian island of Maui, including the town of Lahaina

Gonzalo Marroquin / Getty Images

There is a climatological fact that tends to go unnoticed by the inhabitants of the Southern Hemisphere, who represent around 12% of Earth’s population of 8 billion people: July, the middle of winter for those below the Equator, is usually the hottest month on Earth. The reason for this is related to the geoclimatic features of the two halves of the planet. Because the Northern Hemisphere, which has its summer in the middle of the year, has less ocean surface and twice as much land area as below the Equator, it plays a greater part in determining the planet’s average temperature. Water is a climate moderator, helping to mitigate heat extremes. Thus, when summer in the Northern Hemisphere is very hot — as it has been in recent years — the global temperature rises.

July 2023 confirmed this trend with unprecedented and frightening intensity. Fueled by global warming as a result of increases in greenhouse gas emissions, the seventh month of this year broke several temperature records, sparked forest fires, and caused deaths, especially in the Northern Hemisphere. The most serious event of this scorching period — so far — occurred on the island of Maui, Hawaii, in early August. A fatal combination of hot, dry weather and strong winds spread wildfires to residential areas, killing more than 110 people. The material damage has been estimated at US$5.5 billion and at the time of writing, 1,300 people are still missing.

The final average global temperature figures for July 2023 varied by a few tenths, depending on the historical data and monitoring methodology adopted by the world’s three major climate monitoring agencies. All, however, reached the same conclusion. In July, the planet’s average temperature was around 17 degrees Celsius (°C).

The European Union’s Copernicus Climate Change Service (C3S) reported that the average global temperature in July 2023 was 16.95 °C, the highest observed in any month since records began in 1940. The previous record was set in July 2019, at 16.63 °C. Data from the USA’s National Oceanic and Atmospheric Administration (NOAA) indicated that July 2023 was the hottest July of the last 174 years, with an average temperature of 16.92 °C. It was also probably the hottest month in modern history. “This July was not just warmer than any previous July — it was the warmest month in our record, which goes back to 1880,” said Gavin Schmidt, director of the Goddard Institute for Space Studies (GISS), in a press release issued by the North American Space Agency (NASA), another institution that monitors the global climate.

The average global temperature reached 20.96 ºC on July 31, the hottest day in the planet’s recent history

Heat records were even broken in the Southern Hemisphere, where the winters have been becoming milder for many years. On August 1, the temperature in Buenos Aires exceeded 30 °C, the highest recorded on that day since Argentina’s National Meteorological Service (SMN) began systematically collecting climate data 117 years ago. In northern Chile, temperatures reached 37 ºC, around 15 ºC above normal values for what is normally the coldest period of the year.

With an average temperature of 22.97 °C, this year’s July was the hottest in Brazil since the country’s National Institute of Meteorology (INMET) began recording meteorological data in 1961. This was 0.2 °C higher than the previous record of 22.77 °C measured in July 2022 and 1.04 °C above the historical average for the month. Brazil’s average temperature is calculated using values captured by more than 650 INMET meteorological stations across the country. Automated stations record the temperature every hour, while manned stations take measurements three times a day.

STR / AFP via Getty ImagesChina recorded a maximum temperature of 52.2ºC in JulySTR / AFP via Getty Images

“A set of factors contributed to the rise in temperatures, from changes in land use, with a decrease in vegetation and increase in urbanized areas, to the occurrence of El Niño this year [an abnormal warming of surface waters in the Equatorial Pacific that tends to alter rainfall and temperature patterns in various parts of the world],” points out INMET meteorologist Danielle Barros Ferreira. “But over the past 10 years, the role of climate change in global warming is undeniable.”

An analysis released by the Brazilian National Institute for Space Research (INPE) at the end of August indicated that the current maximum temperature in most of Brazil is 1.5 °C above the historical average recorded between 1960 and 2020. In some areas in the interior of northeastern Brazil and the northwest of the Amazon, temperatures have risen by 2.5 to 3 °C. Similar increases have been recorded in the São Paulo Metropolitan Area. “At a regional level, warming is sometimes much higher than the global average. This occurs not only in Brazil, but in many other parts of the world,” says INPE climatologist Lincoln Muniz Alves, leader of the study.

Alexandre Affonso / Revista Pesquisa FAPESP

According to C3S data, throughout practically all of July this year, the average global temperature was around 1.5 ºC higher than the average value recorded between 1850 and 1900. The second half of the nineteenth century is used as a point of reference for calculating how much the world has warmed since the beginning of the Second Industrial Revolution. The main objective of the Paris Agreement, signed by 195 countries at a United Nations (UN) conference in December 2015, is to encourage the adoption of measures for limiting global warming — defined as the rise in the planet’s average temperature compared to preindustrial levels — to less than 2 ºC, and preferably less than 1.5 ºC.

Each 0.5 ºC increase in Earth’s average temperature has a nonlinear effect on the frequency and intensity of heatwaves, droughts, and heavy rains. It may seem like a small amount, but it can be enough to double or triple the occurrence or intensity of certain weather phenomena.

The 1.5 ºC target would theoretically limit the harm caused to the planet and leave some room to maneuver through the adoption of measures to mitigate and adapt to the climate crisis. The goal, however, seems increasingly out of reach. Greenhouse gas emissions from the burning of fossil fuels and land use changes, such as carbon dioxide (CO2) and methane (CH4), fell slightly at the height of the COVID-19 pandemic between 2020 and 2021, but soon began rising again (see Pesquisa FAPESP issue nº 323).

Léo Ramos Chaves / Revista Pesquisa FAPESPWhile winter in the Southern Hemisphere, such as in São Paulo, was very mildLéo Ramos Chaves / Revista Pesquisa FAPESP

“It is unlikely that we will be able to limit global warming to 1.5 ºC,” says José Marengo, a specialist in climate change and risks from the Brazilian Center for Natural Disaster Monitoring (CEMADEN). “But this fact must not be used as an excuse for not taking immediate action to reduce greenhouse gas emissions.” When examining the NOAA maps that showed temperature variations across the globe in July this year, the climatologist was surprised. They looked a lot like the maps released in the latest reports by the Intergovernmental Panel on Climate Change (IPCC), which were based on somber predictions for the worst-case scenario at the middle of this century.

Current climate models are more efficient at predicting thermal fluctuations and heatwaves than rainfall variations around the world. The formation of rain clouds is a complex process, much more difficult to simulate virtually than the rising and falling temperatures. Many studies highlight this limitation, including an article published by Marengo and colleagues in the International Journal of Climatology in April 2022, in which they compared the effectiveness of 31 climate models at reproducing rainfall and temperature variations that have already occurred in South America and the degree of convergence of their future projections. The results were more consistent at emulating temperature dynamics than rainfall.

Alexandre Affonso / Revista Pesquisa FAPESP

The current heatwave has broken records all over the world. On July 16, China recorded a maximum temperature of 52.2 °C, a temperature never before measured in the country. According to C3S data, July 31, 2023, was the hottest day recorded on the planet since 1940, with the global average temperature reaching 20.96 ºC. The NOAA reported that July 2023 was also the hottest month ever recorded on three continents: Asia, Africa, and South America (in North America, it was the second hottest).

Even at sea there was no reprieve. In July, Antarctica sea ice shrank by 17%, an unprecedented decline, while the average ocean surface temperature hit a record high for the fourth consecutive month in 2023, reaching 0.99 °C above the historical average, according to the NOAA. The North Atlantic has suffered marine heatwaves this year, putting aquatic life at risk. “It has been predicted that 100% of Caribbean corals will be bleached [color loss process] by the end of summer, which could cause mass mortality,” says Regina Rodrigues, an oceanographer from the Federal University of Santa Catarina (UFSC). “As a result of global warming, marine heatwaves have become more frequent, more intense, and longer.”

Pedro SzekelyIce cover in Antarctica was 17% lower in July than the historical averagePedro Szekely

Rodrigues studies the impacts the oceans have on the climate, especially in South America. In addition to El Niño, which warms the eastern Equatorial Pacific and affects rainfall and temperatures, the Atlantic Meridional Overturning Current (AMOC) is one of the most frequent subjects of her research. The AMOC carries warm surface waters from the south of the Atlantic Ocean in Antarctica to the Northern Hemisphere and brings colder, deeper waters to the south from the Arctic. There are indications that global warming will lead to a reduction of the AMOC — maybe even its collapse — within the next few decades. The consequences of its decline could create further problems for the global climate.

The fact that temperature records were broken in so many places around the world in July is a major concern. There is nothing to suggest that this phenomenon is temporary or was an isolated incident. On the contrary, the 10 hottest years in recent history have all occurred since 2010. The year 2016, which marked the end of the strongest El Niño on record, was the year with the highest temperatures according to most climate service surveys. Now, NOAA scientists are estimating that 2023 has a 50% chance of being even hotter.

Alexandre Affonso / Revista Pesquisa FAPESP

“El Niño is just beginning and it’s unlikely that it significantly influenced the current rise in global temperatures,” notes climatologist Carlos Nobre, a senior researcher at the Institute for Advanced Studies of the University of São Paulo (IEA-USP). The biggest impacts of the phenomenon, which has at least an 80% chance of being moderate to strong in intensity, are expected to be felt at the end of the year (see Pesquisa FAPESP issue nº 330). Until March this year, the waters of the eastern Equatorial Pacific were colder than normal due to the influence of La Niña, the inverse phenomenon to El Niño. “We had three years of La Niña, the longest we’ve ever seen,” says Nobre. In theory, cooling in this area of the Equatorial Pacific should mitigate the intensity of global warming. It is possible that it did, but not enough to stop the last three years from making the list of the 10 hottest in history.

At the end of July, when it was almost inevitable that the month would end as the most torrid in recent history, António Guterres, former Prime Minister of Portugal and now Secretary-General of the UN, made a dramatic statement. “The era of global warming has ended; the era of global boiling has arrived. All this is entirely consistent with predictions and repeated warnings. The only surprise is the speed of the change. Climate change is here, it is terrifying, and it is just the beginning.” The way out? Quickly and significantly cutting greenhouse gas emissions and adopting measures to mitigate the impacts of a hotter climate.

INCT for Climate Change (nº 14/50848-9); Grant Mechanism Thematic Project; Program FAPESP Research Program on Global Climate Change (PFPMCG); Principal Investigator José Antônio Marengo Orsini (CEMADEN); Investment R$4,389,577.78.

Scientific article
GOUVEIA, C.D. et al. Uncertainties in projections of climate extremes indices in South America via Bayesian inference. International Journal of Climatology. vol. 42, no.14. apr. 11, 2022.