The Heat Goes On: New Details Emerge About the Extent and Severity of Record-Setting Global Warmth

In Part 1 of this three-part series focusing on a new report about climate change in 2023, I described the relentless rise of greenhouse gases in the atmosphere. Rather than showing signs of leveling off — which must happen soon if we are to avoid even more disruptive climate changes than we've already seen — they're accumulating at an increasing rate.

In fact, 2023 saw the fourth highest rise of atmospheric CO2 on record.

As I pointed out in Part 1, no aspect of Earth's climatic life support system was spared last year from the impact of the ever thickening blanket of heat-trapping gases we've thrown over the planet, according to the State of the Climate in 2023 report. That, of course, includes rising temperatures worldwide, which I focus on here. (For links to the other articles in this series, see the end of this story.)

To put it bluntly, global heating was completely off the charts in 2023. In records dating back as far as 1850, the annual global average surface temperature was by far the highest ever observed.

Analysis of seven separate datasets revealed that the global surface temperature in 2023 was 0.55°C–0.60°C above the 1991–2020 average. This was the highest value on record, surpassing the previous warmest year on record, 2016, by a large margin.

The State of the Climate analysis also compared 2023's global average temperature to what it was in pre-industrial times, before humankind began spewing large amounts of greenhouse gases into the atmosphere. According to the report, the global surface temperature last year was 1.35°C–1.54°C above that pre-industrial average.

"Dozens of countries reported record or near-record warmth for the year, including China and continental Europe as a whole (warmest on record), India and Russia (second warmest), and Canada (third warmest)," the report states. Moreover, "intense and widespread heatwaves were reported around the world."

The unusual global heating in 2023 wasn't just a one-off. All seven datasets agree that 2015 through 2023 were the nine warmest years since global record-keeping began. And the heat has gone on — and on: Every month through July of this year has seen record-setting global temperatures, according to NOAA.

Here in 2024, last month was the warmest July globally in NOAA's 175-year record. This marks the 14th consecutive month of record-high global temperatures, breaking the longest record warm streak in the modern record. The previous record global heat streak was set from May 2015 through May 2016.

Ocean Heating

From 1971 through 2020, the seas have absorbed about 89 percent of the heat that has entered our planet's climate system as a result of our emissions of greenhouse gases. The State of the Climate in 2023 report notes that the buildup of this heat has been greatest at the surface — and it really shows:

In 2023, global temperatures at the sea surface shattered the previous record high. And record-breaking sea surface temperatures continued into 2024, only showing signs of decline in recent weeks.

As an aside, that cooling trend is likely to continue as a La Niña takes hold. The climate phenomenon is characterized by cooler than average sea surface temperatures in the tropical Pacific Ocean, and it tends to tamp down global averages.

But climate models have been suggesting we'll experience a weaker and delayed onset of La Niña than previously thought.(For the latest on this, check out this post at the ever-excellent ESNO blog: August 2024 Outlook: A La Niña Watch in the Dog Days of Summer.)

Back to 2023: The new report revealed that a shocking 94 percent of the global ocean surface experienced at least one marine heat wave. These transient periods of exceptionally high ocean temperatures can super-charge tropical cyclones, while bleaching corals and harming ocean ecosystems, including fisheries that millions of people around the world depend on for food.

Typically, at any given location, marine heatwaves are observed about 10 percent of the time. But according to the report, in 2023 these events far exceeded what's considered typical, "with record-breaking extremes (in terms of area coverage and intensity) observed all over the world."

In total, 2023 saw a record of 116 marine heatwave days during the year, blowing away the previous record of 86 days set in 1982.

Marine ecosystems have suffered greatly, as revealed by the severity and extent of coral bleaching. This can happen when corals are stressed so much by warm sea temperatures that they expel the symbiotic algae living with them, causing them to turn ghostly white. Although bleached corals can survive, they can ultimately die if the stress is too high and sustained.

During 2023, bleaching of corals worldwide was particularly severe — and it continued into this year. According to a recent report from NOAA, since the beginning of 2023 and continuing at least through mid-May 2024, mass coral bleaching had been confirmed in all ocean regions where warm-water corals live, and in at least 62 countries and territories worldwide.

Coming up next...

The unusually high degree of global heating in 2023 was accompanied by myriad other impacts, including accelerating ice loss, rising sea level, changes in cloudiness, decreased precipitation on average but heavier short-term deluges, and spreading drought. I focus on these impacts in the final installment of this series.

For Part 1 of the series, please go here. And for Part three click here.