Ocean heat content (OHC) reached record levels in 2023
How do we know if the climate change is real? If you are me, you are appalled with the state of the world today. You can point to increased frequency of wildfires, draughts and floods, heat waves and sea level rise. Skeptics, however, will be quick to find out examples of ‘cooler’ years in the recent past to show that climate change isn’t real.
This is because although there is an upward trend of mean surface temperature, there is natural variability due to El-Nino and La-Nina events, volcanoes and monsoons. If the summer is unusually hot this year, how much of it can be attributed to global warming?
Therefore, to measure climate change, we need an indicator that shows a steady trend (i.e. signal) and is unaffected with temporal factors (i.e. noise). In other words, the indicator should have a strong signal to noise ratio.
Oceans cover seventy percent of the earth and naturally absorb most (over 90%) of the heat from greenhouse gases. Ocean heat content (OHC) is a variable that measures energy trapped by the oceans which has been steadily rising over the past few decades. That is true irrespective of whether the current year is warmer or cooler. OHC, hence, is a robust indicator of climate change.1
Surface temperatures are breaking all records with May 2024 being the 12th consecutive hottest month till date.2 OHC continued the upward trend since 1960 and recorded the highest value till date in 2023. 3
If our planet is a body, oceans are its heart. Ocean currents act like a conveyor belt and control the weather throughout the earth.4 High OHC is linked to increased heat transfer towards poles and reduced mixing with deeper waters.5 The effects are visible- Arctic is heating up four times than rest of the planet6 and gulf stream is at its weakest.7
We already know the solution. Pick up your shovel and start removing (and reducing) as much carbon you can find.
Cheng, L., Abraham, J., Trenberth, K.E. et al. New Record Ocean Temperatures and Related Climate Indicators in 2023. Adv. Atmos. Sci. 41, 1068–1082 (2024). https://doi.org/10.1007/s00376-024-3378-5
Thomas J F Goreau, Raymond L Hayes, 2023 Record marine heat waves: coral reef bleaching HotSpot maps reveal global sea surface temperature extremes, coral mortality, and ocean circulation changes, Oxford Open Climate Change, Volume 4, Issue 1, 2024, kgae005, https://doi.org/10.1093/oxfclm/kgae005