July Hottest Month Ever in Northern Hemisphere

ON 08/01/2023 AT 03:17 PM

July was the hottest month in known human history for the northern half of the planet.

Daily High Temps 2023 August 01

Image: Birkel, S.D. 'Today's Weather Maps', Climate Reanalyzer, Climate Change Institute, University of Maine, USA.

Intense heat is gripping large parts of the Northern hemisphere in this summer of extremes, causing major damage to the people’s health and the environment. China set a new national daily temperature record, and many new station temperature records have been broken around the globe.

The physics of global warming are very simple. Certain atmospheric gases block energy from the sun from being reflected back into space. As the concentration of those gases increases, the temperature of the Earth increases, but that also means the redistribution of cold and some places actually may get a bit colder for short periods of time. There were numerous record lows this last winter for cold, just as there were countless record highs.

The increasing temperatures wreak havoc on the planet and this is called climate change. But it is not just the climate that is changing. Ocean levels are rising, major ocean currents are changing or shutting down, glaciers around the globe are melting, there are both severe droughts and unprecedented floods in the same regions, forests and wetlands that were once carbon sinks have become carbon emitters and forests around the world are burning up. 

In July, wildfires have caused devastation and dozens of casualties and forced evacuations of thousands of people in parts of the Mediterranean, including Algeria, Greece, Italy and Spain. The Copernicus Atmosphere Monitoring Service (CAMS) has recorded a significant increase in intensity and emissions from wildfires in the eastern Mediterranean during the second half of July, particularly in Greece. In accordance with the GFAS dataset, the emissions from these wildfires have been the highest for this period of time in Greece in the last 21 years. Canada has seen its worst wildfire season on record, harming air quality for millions of people in North America.

Sea surface temperatures have hit new records, with severe marine heatwaves in the Mediterranean and off the coast of Florida.

“The extreme weather — an increasingly frequent occurrence in our warming climate — is having a major impact on human health, ecosystems, economies, agriculture, energy and water supplies. This underlines the increasing urgency of cutting greenhouse gas emissions as quickly and as deeply as possible,” said World Meteorological Association (WMO) Secretary-General Prof. Petteri Taalas.

“In addition, we have to step up efforts to help society adapt to what is unfortunately becoming the new normal. The WMO community is providing forecasts and warnings to protect lives and livelihoods as we strive to achieve our goal of Early Warnings for All,” said Prof. Taalas.

A rapid study from climate scientists in the World Weather Attribution network said that the heatwaves bore the clear footprint of climate change.

“Without human induced climate change these heat events would however have been extremely rare. In China it would have been about a 1 in 250 year event while maximum heat like in July 2023 would have been virtually impossible to occur in the US/Mexico region and Southern Europe if humans had not warmed the planet by burning fossil fuels,” said the attribution study published on 25 July.


Heatwaves are amongst the deadliest natural hazards with thousands of people dying from heat-related causes each year. The full impact of a heatwave is often not known until weeks or months afterwards, WMO experts told a media briefing on 18 July.

France, Greece, Italy, Spain, Algeria and Tunisia reported new maximum daytime and overnight station temperature records.

For instance, Figueres (Catalonia), reported a new temperature record of 45.4 °C on 18 July (provisional all-time maximum). A station on the Italian island of Sardinia recorded 48.2°C on 24 July.

In Algeria and Tunisia, the highest maximum temperature was respectively 48.7 °C (Dar El Beïda/Argel) and 49.0 °C (Tunis and Kairouan) on 23 July.

In some parts of the Mediterranean, a further continuation of the extreme heat into August is possible, said a Climate Watch Advisory issued by the Climate Monitoring node of the WMO’s Regional Climate Centre for Europe, operated by the Deutscher Wetterdienst (DWD), the German Weather Service. It is designed as guidance for National Meteorological and Hydrological Services which are responsible for forecasts and warnings in their own territory. 

"An increasing number of studies demonstrate connections between rapid warming and the Arctic and mid-latitude weather patterns, including in atmsopheric dynamics such as the jet stream. The jet stream becomes weaker and wavier when warm air is transported to the north and cold air to the south. In these conditioins, near-stationary weather patterns establish and lead to prolonged heatwaves and drought in some regions and heavy precipitation in others," said Alvaro Silva, an expert with WMO climate services division.

Sanbao weather station in Turpan city in China's Xinjiang province, had a temperature of 52.2°C on 16 July, setting a new national temperature record according to a report by the China Meteorological Administration.

North America

Large parts of the USA also were gripped by extensive heatwaves, with high temperatures in numerous places, according to the US National Weather Service, which says a few locations could even register their all-time temperature records. 

The US National Weather Service issued repeated excessive heat warnings and advisories, often covering more than 100 million people. In the latest update issued on 31 July, it warned that the dangerous heat in the affected areas would continue through 5 August.

In South-Central and Southeast USA, maximum heat index values could near or exceed 110 ° Fahrenheit (43° C). Many parts of Florida, including the city of Miami, have been hit by an extended, record-breaking heatwave.

Phoenix, Arizona, recorded 31 days, as of 30 July, of daytime temperatures above 110 °F (43.3 °C). Overnight low temperatures were repeatedly more than 90°F (32.2°C), according to the National Weather Service. 

"We need to broaden focus beyond maximum temperatures because the minimum temperature is most important for health and critical infastructure," said WMO extreme heat senior advisor John Nairn.

A temperature sensor at Furnace Creek in Death Valley National Park in California recorded 128 °C (53.3°C) on 16 July.  

According to the WMO Archive of Weather and Climate Extremes, the hottest temperature ever recorded was in Furnace Creek, Death Valley, California at 56.7°C on 10 July 1913.


Wildfires forced the evacuation of hundreds of residents and tourists on the Greek islands of Rhodes, Evia and Corfu since 17 July. The emissions of these wildfires have reached record levels, with an estimated total of 1 megaton of carbon emissions between 1 July and 25 July, almost doubling the July 2007 record, following several days of high intensity fires, according to Copernicus Atmospheric Monitoring Service.

In Algeria, there were several dozen reported casualties.

Hot, dry conditions have fueled an early an intense wildfire season in Canada (since the spring). The fires have forced more than 120 000 people to evacuate their homes and polluted the air for millions of people across North America.

In Canada, record-breaking wildfires continue to burn big forest areas. More than 650 wildfires were out of control as of 24 July. According to the Canadian Interagency Forest Fire Centre more than 11 million hectares already burnt in 2023 – compared to the 10-year average of about 800,000 hectares.

The record levels of emissions generated by the intense wildfire activity across Canada in May and June had a major impact on air quality, both in Canada and further afield. According to CAMS data, fire radiative power (FRP) for the country as a whole in the first three weeks of June was significantly higher than the 2003-2022 mean, with estimated carbon emissions at over 100 megatonnes for the month. Emissions levels from the start of the year until the first week of May remained close to the 2003-2022 mean, but then quickly rose to significantly higher than any previous year in the CAMS record (see right-hand graph below).

The fires continued to rage at the end of July, with numerous fires breaking out within Canada's Arctic circle.

Marine Heatwaves

Daily Sea Surface Temps 01 August 2023

Image: Birkel, S.D. 'Today's Weather Maps', Climate Reanalyzer, Climate Change Institute, University of Maine, USA.

Sea surface temperatures (SSTs) of the Mediterranean Sea are exceptionally high over the coming days and weeks, exceeding 30 °C in some parts, and more than 4 °C above average in a large part of the western Mediterranean.

Unconfirmed reports said that Manatee Bay, Florida, recorded a sea surface temperature of 101.1°F (38.4°C) – warmer than a hot bath.

The impacts of marine heatwaves impacts include migration of species and extinctions, arrival of invasive species with consequences for fisheries and aquaculture.

Heavy rains and floods

Heavy rains and flooding caused severe damage and loss of life in several parts of the world.

Forty people were reported killed as torrential rain and flash floods hit the Republic of Korea on 14 July.

Floods in Northwest China killed a reported 15 people, prompting dictator Xi Jinping to urge greater efforts to protect the public from extreme weather.

In northern India, roads and bridges collapsed and houses were swept away as rivers overflowed during heavy monsoonal rainfall and flooding which killed dozens of people. The mountainous state of Himachal Pradesh was badly hit, as were the regions of Punjab, Rajastan and Uttar Pradesh. New Delhi reportedly marked its wettest July day in 40 years, with 153 millimeters (6 inches) of rain falling in one day.

The Japanese Meteorological Agency (JMA) issued heavy rain emergency warnings for the Fukuoka and Oita prefectures, on Kyushu, the country’s third largest island. A new daily rainfall record of 376.0 mm fell on 10 July at Minousan and 361.5 mm at Hikosan, both in the Kyushu region.

In Northeastern USA, parts of New England faced yet more torrential rainfall on saturated soils following serious floods at the start of July. New York issued a flash flood emergency and more than four million people were under floods alerts on 11 July. The Canadian province of Nova Scotia received three months worth of rain in 24 hours on July 22nd, which caused extensive damage and killed at least four people.

"As the planet warms, the expectation is that we will see more and more intense, more frequent, more severe rainfall events, leading also to more severe flooding,” said Stefan Uhlenbrook, Director of hydrology, water and cryosphere at WMO.