Climate-scale analysis of changing air and water masses

Lead Research Organisation: University of Southampton
Department Name: School of Ocean and Earth Science

Abstract

This project is concerned with measuring changes in global rainfall and ensuring that computer models of the climate can predict how rainfall will change in the future.

As carbon dioxide and other greenhouse gases are continually added to the atmosphere, it is understood that the temperature of the surface of the earth will rise. Warmer air can hold more moisture, so as the Earth warms the rate at which the atmosphere extracts water from the surface of the earth and dumps it back as rain will also increase. Knowing precisely how much global rates of rainfall will change into the future is important to many people including farmers wanting to know which crops to plant and nations wanting to build domestic water and hydroelectric infrastructure.

Measuring the total rainfall around the world is no mean feat. On land, measurements are made directly (by catching the rain) or by reliable 'indirect' methods based on river flow and how wet the soil is. However, two-thirds of the globe is covered by ocean. It is hard to catch rain in the middle of the ocean without actually being there to do it. Although many 'indirect' methods exist for measuring rainfall over the ocean there is great uncertainty about how much rainfall has changed over the ocean in the last 50 years or so.

Thankfully there is a solution. The ocean itself acts as a giant rain catcher. Water that falls as rain is fresh water, like the water we drink. Most of the ocean however, is very salty. So the more rain that falls, the fresher the ocean water gets and the more evaporation that occurs the saltier the ocean water gets. Oceanographers can measure just how salty the water in the ocean is and have been doing so regularly for more than 50 years now. The question remains however, how do you turn measurements of the salinity of the ocean into measurement of how much rain has fallen?

Well, by looking all around the globe and counting up how much more salty water there is and how much fresh water there is, researchers can estimate how much water has been evaporated in one place and fallen as rain in another. The researchers involved in this project will do this using all the observations of salinity in the ocean taken over the last 50 years. They will estimate just how much rainfall has changed. They will compare this with computer models which are commonly used to predict what will happen in the future to see how accurate they are and how they can be improved.

Planned Impact

Understanding the water cycle is of fundamental societal importance. Rainfall and evaporation influence food security, extreme events, public health, energy, and ultimately the habitability of many regions of the globe.

The hypothesis presented in this study is that the change in the water cycle experienced by the climate system over the last 50 years is larger (more rainfall and more evaporation) than that predicted by the current generation of IPCC class climate models. We hypothesise that there is not only disagreement between models, but that these models may be consistently biased towards weaker hydrological cycle responses.

If this hypothesis is confirmed or if additional weight is brought to it, the impact will be far reaching. Organisations which make use of IPCC predictions of hydrological cycle change will learn more about their accuracy. Governments, agricultural firms, global insurers and organisations concerned with global health and security will all be impacted.
 
Description We have developed new methods to relate ocean salinity to water cycle change.

We have found that the water cycle is amplifying at approximately 3%-4% per Kelvin or half the maximum water vapour increase predicted by the Clausius Clapeyron equation.

We have validated the methods used against state of the art climate models. We also compared salinity and water cycle changes in the state of the art models to observations. Contrary to recent published findings our results suggest the climate models are consistent in terms of their large scale water cycle change.

In addition, with Project Partners in Canada and Sweden, we have shown that increases in the water cycle may constrain the work output of the atmospheric heat engine. That is, potentially stop the atmosphere from getting windier with global warming.

Using carefully designed model experiments, we have attributed changes in the global salinity pattern to three drivers: around one half due to water cycle change (which amplifies salinity differences); around one third due to upper ocean warming (which reduces mixing away of salinity contrasts); around one sixth due to ice mass loss (which reduces the salinity of already fresh regions). This refines our use of salinity "pattern amplification" as a measure of the changing water cycle at global scale.
Exploitation Route Methods to relate salinity changes to rainfall/evap changes will be important for monitoring climate and calibrating forecasts on short and long timescales.

The finding that the water cycle is changing is important for detection, monitoring and adaptation to climate change. Knowing that climate models are predicting a response consistent with observations adds confidence to their future projections. This helps policy makers and the public to make decisions based on climate projections.

The fundamental finding that the water cycle will constrain the work output of the atmosphere has potentially significant impacts on how society prepares for a changing climate.
Sectors Agriculture, Food and Drink,Energy,Environment,Government, Democracy and Justice

URL https://www.southampton.ac.uk/oes/research/projects/
 
Title Analysis of changing water cycle and water mass properties at regional & global scales 
Description Ocean observations and model output are analysed for changes in climate, including the global water cycle, using a new theoretical framework. 
Type Of Material Data analysis technique 
Provided To Others? No  
Impact Using this method, we have found that the global water cycle is intensifying at around half the rate previously predicted (Skliris et al. 2016, Scientific Reports). 
 
Description Water mass transformation framework - review and international workshop 
Organisation National Oceanic And Atmospheric Administration
Department Geophysical Fluid Dynamics Laboratory (GFDL)
Country United States 
Sector Public 
PI Contribution We hosted a 2-day workshop at the National Oceanography Centre, 23-24 August 2016, attended by Dr Daniele Iudicone (Stazione Zoologica Anton Dohrn), Dr Sjoerd Groeskamp (then Columbia University, now University of New South Wales), Dr Jan Zika (now University of New South Wales), Dr George Nurser (NOC) and Prof Robert Marsh (U. Southampton), to discuss a review paper on the water mass transformation framework (central to CLAW) that is now widely used in marine science, 35 years since the first recognized paper in this research area. This led to a review paper Annual Reviews of Marine Science, and a 35-participant international workshop in February 2019, attended by Zika, Marsh and Nurser.
Collaborator Contribution Dr Iudicone and Dr Groeskamp led the review, now published in Annual Reviews of Marine Science. Dr Grosekamp organised "Water Mass Transformation for Ocean Physics and Biogeochemistry Workshop", 4-6 February 2019, University of New South Wales, Sydney, Australia; the workshop was attended by 35 participants from the international community of ocean physics and biogeochemistry.
Impact Groeskamp, S., Griffies, S.M., Iudicone, D., Marsh, R., Nurser, A.G., and J.D. Zika (2019). The water mass transformation framework for ocean physics and biogeochemistry. Ann. Rev. Mar. Sci., 11 (1), 271-305. International workshop, "Water Mass Transformation for Ocean Physics and Biogeochemistry Workshop", 4-6 February 2019, University of New South Wales, Sydney, Australia; this was a multi-disciplinary workshop, bringing together physical oceanographers and biogeochemists
Start Year 2016
 
Description Water mass transformation framework - review and international workshop 
Organisation Stazione Zoologica Anton Dohrn
Country Italy 
Sector Private 
PI Contribution We hosted a 2-day workshop at the National Oceanography Centre, 23-24 August 2016, attended by Dr Daniele Iudicone (Stazione Zoologica Anton Dohrn), Dr Sjoerd Groeskamp (then Columbia University, now University of New South Wales), Dr Jan Zika (now University of New South Wales), Dr George Nurser (NOC) and Prof Robert Marsh (U. Southampton), to discuss a review paper on the water mass transformation framework (central to CLAW) that is now widely used in marine science, 35 years since the first recognized paper in this research area. This led to a review paper Annual Reviews of Marine Science, and a 35-participant international workshop in February 2019, attended by Zika, Marsh and Nurser.
Collaborator Contribution Dr Iudicone and Dr Groeskamp led the review, now published in Annual Reviews of Marine Science. Dr Grosekamp organised "Water Mass Transformation for Ocean Physics and Biogeochemistry Workshop", 4-6 February 2019, University of New South Wales, Sydney, Australia; the workshop was attended by 35 participants from the international community of ocean physics and biogeochemistry.
Impact Groeskamp, S., Griffies, S.M., Iudicone, D., Marsh, R., Nurser, A.G., and J.D. Zika (2019). The water mass transformation framework for ocean physics and biogeochemistry. Ann. Rev. Mar. Sci., 11 (1), 271-305. International workshop, "Water Mass Transformation for Ocean Physics and Biogeochemistry Workshop", 4-6 February 2019, University of New South Wales, Sydney, Australia; this was a multi-disciplinary workshop, bringing together physical oceanographers and biogeochemists
Start Year 2016
 
Description Water mass transformation framework - review and international workshop 
Organisation University of New South Wales
Country Australia 
Sector Academic/University 
PI Contribution We hosted a 2-day workshop at the National Oceanography Centre, 23-24 August 2016, attended by Dr Daniele Iudicone (Stazione Zoologica Anton Dohrn), Dr Sjoerd Groeskamp (then Columbia University, now University of New South Wales), Dr Jan Zika (now University of New South Wales), Dr George Nurser (NOC) and Prof Robert Marsh (U. Southampton), to discuss a review paper on the water mass transformation framework (central to CLAW) that is now widely used in marine science, 35 years since the first recognized paper in this research area. This led to a review paper Annual Reviews of Marine Science, and a 35-participant international workshop in February 2019, attended by Zika, Marsh and Nurser.
Collaborator Contribution Dr Iudicone and Dr Groeskamp led the review, now published in Annual Reviews of Marine Science. Dr Grosekamp organised "Water Mass Transformation for Ocean Physics and Biogeochemistry Workshop", 4-6 February 2019, University of New South Wales, Sydney, Australia; the workshop was attended by 35 participants from the international community of ocean physics and biogeochemistry.
Impact Groeskamp, S., Griffies, S.M., Iudicone, D., Marsh, R., Nurser, A.G., and J.D. Zika (2019). The water mass transformation framework for ocean physics and biogeochemistry. Ann. Rev. Mar. Sci., 11 (1), 271-305. International workshop, "Water Mass Transformation for Ocean Physics and Biogeochemistry Workshop", 4-6 February 2019, University of New South Wales, Sydney, Australia; this was a multi-disciplinary workshop, bringing together physical oceanographers and biogeochemists
Start Year 2016