How September Became the Hottest Month Ever and What It Means for Our Future

The Record-Breaking Heat

September 2023 was the most anomalously warm month ever recorded, meaning it was much hotter than the average for that month.
September 2023 was about 0.5 degree C (0.9 degree F) hotter than the previous hottest September in 2020, and about 0.2 degree C (0.4 degree F) warmer than the previous record high temperature anomaly in February 2016.
This September was hotter than most Julys before the last decade or two, which shows how much global temperatures have risen in recent decades.

The main cause of the extreme heat is the increase of greenhouse gases in the atmosphere from burning fossil fuels, which trap heat and warm up the planet.
Another factor is an El Niño event, which is a natural climate cycle that features unusually warm waters in the eastern Pacific Ocean. El Niño can release more heat into the atmosphere and affect weather patterns around the world.
Some minor factors are the phasing out of sulfur-containing fuels used by ships, which have a slight cooling effect, and the eruption of a volcano in the southern Pacific Ocean last year, which injected water vapor, another greenhouse gas, into the atmosphere.

The rising temperatures have caused many heat waves around the globe, some of which were found to be virtually impossible without global warming. These heat waves can have harmful effects on human health, agriculture, and ecosystems.
The rising temperatures also increase the risk of other extreme weather events, such as droughts, floods, storms, and wildfires, which can cause damage and displacement.
The rising temperatures also threaten to melt ice sheets and glaciers, raise sea levels, and change ocean currents and chemistry, which can have serious consequences for coastal communities and marine life.

The world has agreed to try to limit global warming to 1.5 degrees C (2.7 degrees F) above preindustrial levels under the Paris climate accord. This is a level that scientists consider to be relatively safe and manageable.
However, 2023 or 2024 could be the first year to exceed that threshold, which means we are running out of time to take action. Even if we do exceed that threshold in a single year, we still have a chance to keep it below that level on average over several decades.
To limit global warming, we need to reduce our emissions of greenhouse gases by switching to clean and renewable energy sources, improving energy efficiency, and adopting low-carbon lifestyles. We also need to enhance our resilience and adaptation to the impacts of climate change that are already happening or unavoidable.
Every bit of carbon we can keep or take out of the atmosphere is crucial. Every tenth of a degree matters. We need to act fast and ambitiously to avoid the worst-case scenarios of climate change.