An Argo float at the surface of the ocean. During this time, it will transmit that data it collected on its last pass through the water column.

By Claire

There is a belief by some members of the public that climate change models are seriously over-predicting the possible impacts of climate change, leading to unnecessary worry and unfounded claims.

While I could go on for a while about why this isn’t the case, I think it holds more weight when it comes straight from the scientists who work on and verify climate models.

A recent study published in Science, shows that the hydrological cycle has intensified over the last 50 years at twice the rate as that predicted by climate change models.

This study focusses on data gathered from Argo floats. Argo floats are automated ocean profiling devices, which measure temperature and salinity from 2000 m depth to the surface every 10 days. Argo floats are free moving, and cover the majority of the world’s oceans, particularly in areas where ship-based sampling is not practical, such as the Southern Ocean.

Data from these floats provides a snapshot of the global hydrological cycle, through the understanding of the spatial and temporal distribution of high and low salinity waters. In areas with high evaporation, salt is left behind in surface waters, leading to more saline conditions. In areas with high precipitation, fresh rainwater dilutes seawater, leading to less saline conditions.

Wijffels and colleagues have found that the difference between the saltier and fresher areas have become more marked in the past 50 years, indicating that more water is being pumped through the global cycle.

“We’ve been able to pick up a very strong and clear fingerprint of the accelerating water cycle in the ocean salinity field,” says Wijffels.

While these findings are significant on their own, scientists have been able to compare these observed results with climate model predictions of changes to verify the model output.

“The models predict a 4 to 5 per cent amplification of the global water cycle per degree of warming, instead of 8 per cent,” says Wijffels.

“It’s a significant underestimation. That’s a cause for concern.”

Modeled (yellow) and observed (black) temperature for the last 100 years. Notice that the observations are following model predictions very closely.
Source: IPCC

Unfortunately, when we look at observations of current climate, we see that model projections are in fact underestimating the impacts of climate change on some parts of climate. While this may not be the case for all climate indicators, current observed temperature changes suggest that visions of a future affected by climate change are more realistic than we might want to believe.

Listen to an interview with the authors here.