Ocean data 1950 to 2000

The question of how bad global warming will get has long been cast in terms of how hot the world will get. But perhaps more important will be how much rising greenhouse gases crank up the water cycle. Theory and models predict that a strengthening greenhouse will increase precipitation where it is already relatively high and decrease it where it is already low. A new study of the ocean’s changing salinity in the April Science journal confirms that this mechanism of water-cycle amplification has been operating for the past half-century. The result also suggests that the water cycle is intensifying quickly under global warming—twice as fast as climate models have been predicting.

The study, published in the April edition of the journal, has concluded that climate change is altering oceans and rainfall worldwide. A team of three researchers looked at ocean data over the period 1950 to 2000. They found salinity levels have changed in all the world’s oceans, wetter areas are experiencing more rain and drier areas have become drier.

One of the researchers, Susan Wijffels from the CSIRO, is co-chair of the Argo project, a global array of 3,500 free-drifting profiling floats that measures the temperature and salinity of the upper 2000m of the ocean.  This allows, for the first time, continuous monitoring of the temperature, salinity, and velocity of the upper ocean, with all data being relayed and made publicly available within hours after collection.

Dr Wijffels says she expects these documented trends to continue. “The answer of how much more is going to be in the future depends on how much more warning there is going to be,” she said. “So if we stay on a high emissions pathway we might see warming up around three degrees, which will give us maybe a 24 per cent change in our water cycle.”

More past the link if you want the detail…

The authors say this could have implications for global food security. A two minute news item from ABC tv online here.

Their abstract reads… Fundamental thermodynamics and climate models suggest that dry regions will become drier and wet regions will become wetter in response to warming. Efforts to detect this long-term response in sparse surface observations of rainfall and evaporation remain ambiguous. We show that ocean salinity patterns express an identifiable fingerprint of an intensifying water cycle. Our 50-year observed global surface salinity changes, combined with changes from global climate models, present robust evidence of an intensified global water cycle at a rate of 8 ± 5% per degree of surface warming. This rate is double the response projected by current-generation climate models and suggests that a substantial (16 to 24%) intensification of the global water cycle will occur in a future 2° to 3° warmer world.