New methods are improving ocean and climate measurements | John Abraham

Improvements to ocean temperature measurements are making good measurements great

I have often said that global warming is really ocean warming. As humans add more heat-trapping gases to the atmosphere, it causes the Earth to gain energy. Almost all of that energy ends up in the oceans. So, if you want to know how fast the Earth is warming, you have to measure how fast the oceans are heating up.

Sounds easy enough at first, but when we recognize that the oceans are vast (and deep) we can appreciate the difficulties. How can we get enough measurements, at enough locations, and enough depths, to measure the oceans’ temperatures? Not only that, but since climate change is a long-term trend, it means we have to measure ocean temperature changes over many years and decades. We really want to know how fast the oceans’ temperatures are changing over long durations.

We can see the effects of climate change in our oceans. To do this, we measure changes in temperature in our oceans over decadal time scales. Measuring the temperature of ocean water is not a new thing, it has been done for hundreds of years, and over time, measurement techniques have changed. In modern times, the XBT has been used extensively to measure ocean temperature and is only one of many methods. XBT data is special because it comprises ~50% of historical data between 1967 and 2001, a huge resource for oceanographers and for estimates of decadal changes in ocean temperature.

Small biases in the historical XBT data have been identified and various bias corrections have been developed which greatly improve the XBT data for climate change estimates. This work focusses on a purely physical method to estimate a fall rate for the XBT, which is unusual in the field of bias correction estimates. By looking at the physical shape of the XBT probe the fall rate is modelled. Other bias correction studies have looked at comparisons between XBTs and other instruments.