World’s oceans capturing unrelenting climate change

1 Sep 2022 12:11 PM

The world’s oceans are charting the unrelenting progress of climate change says a new global report: The State of the Climate in 2021.

The 32nd annual State of the Climate report – published yesterday by the Bulletin of the American Meteorological Society – shows that two marine-related measures – ocean heat content and global sea level rise – were the highest on record last year.

Scientists measure climate change by a number of different means. Measuring the Earth’s surface temperature is the most familiar method and is the one linked to global action on climate change, such as the Paris Agreement.

The Met Office’s Dr Robert Dunn has been the lead editor of the report’s Global Climate chapter for several years. Commenting on this year’s report he said: “By measuring Earth’s surface temperature since 1850 we know that 2021 was one of the six hottest years since records began. However, natural variations including planetary cycles – such as the temporary cooling of the tropical Pacific during the recent La Niña event – can mask some of the detail of climate change when using only the surface temperature as a metric.

“But when you look at how much the deep ocean is warming and how much sea levels are rising it is easier to obtain a clearer trend of ongoing climate change, as the majority of the excess energy trapped in the climate system by increases in greenhouse gases goes into heating the oceans. For these two measurements 2021 was a record-breaking year.”

Ocean heat content and sea level rise are important components of the climate system. The ocean has the largest heat capacity on earth and more than 90% of the extra heat goes into increasing ocean heat content. Sea level rise – led by the thermal expansion of water and melting glaciers and ice caps – is an important consequence of climate change.

Robert Dunn yesterday concluded:

“The evidence of climate change becomes more stark with the publication of every annual State of the Climate report. If we can get to a point where atmospheric greenhouse gas concentrations start to flatline or even reduce, we would in time start to see a much more positive picture of our climate and our future from these reports.”

The State of the Climate report details:

The State of the Climate report is a peer-reviewed series published annually as a special supplement to the Bulletin of the American Meteorological Society. It is available online here.

The Met Office also tracks key global climate indicators on its Global Climate Dashboard.