Global WarmingAnd the

Planetary Water Cycle

Ruth CurryWoods Hole Oceanographic InstitutionRuth CurryWoods Hole Oceanographic Institution

Global WarmingAnd the

Planetary Water Cycle

Planet Earth is warming

290

190 ppm

The link between greenhouse gas concentrations and surface temperatures is indisputableYou are

here

379

Penetration of ocean warming signal

Courtesy of Tim Barnett (Scripps)

In the last half of the 20th century, it is clear that the world oceans are heating up.

Levitus et al. Science, 2005

The oceans have absorbed about 20 times more heat than the atmosphere since 1955

Oceans 14.5 x 1022 J

Atmosphere 0.7 x 1022 J

Global climate change is not just about temperature….

A snowman’s perspective

It is expected that the planetary water cycle – Evaporation/Condensation/Precipitation and

Freezing/Melting – will be altered as a result of global warming.

There is ample evidence of it already happening…

Precipitation patterns are changing on global scales…

…most measurements of precipitation are made over land areas

Unprecedented warmth of SST in Indian, W. Pacific and Atlantic Oceans is driving shifts in precipitation patterns…

Salinity changes are the fingerprint ofincreasing evaporation from the low

latitude oceans…..

Low latitude surface waters have become markedly more saline

Water masses formed at high latitudes have become fresher

… and freshwater being added to the oceans at high latitudes.

Atlantic Ocean Salinity Changes1990s compared to 1960s

from Curry et al. Nature (2003)

Increased river dischargeIncreased precipitationappears to be the dominantfactor elevating continentalrunoff into the Arctic basinswhich is contributing to salinity decreases in the North Atlantic

19791979

20002000

NASA Goddard Space Flight Center

Summer Arctic Sea Ice

is shrinking and thinning

NY Times June 8, 2004

Greenland is melting

Antarctica is still gaining mass, but its ice shelves are growing unstable,

increasing the surge of land ice into the ocean

Ocean warming and melting land ice are causing sea level to rise

Too much freshwater added to key locations could disrupt ocean circulation and its transport

of heat

Conveyor ON

Conveyor OFF

North SouthDenmark Strait North South

Denmark Strait

… and changing the density of waters that feed the overflows – the first steps toward slowing the Ocean Conveyor

Since the 1990s, freshwater has been accumulating in the surface layers of the Nordic Seas …

Freshwater storage and net flux anomalies

Curry & Mauritzen, Science (2005).

19000 km3

4000 km3

15000 km3

0.066 Sv

10,000 km3

This does not mean the Ocean Conveyor will shut down, but that conditions are

moving in a direction favorable for doing so.

Conveyor ON Conveyor OFF

Earth’s freshwater balance is being pushed out of kilter by rising GHG concentrations, and this is expected to amplify in the foreseeable future.

A scientist’s perspective:

Sea level rise and freshwater resources will be issues of increasing urgency confronting ecosystems and economies in the 21st century.

It is not a question of “if”….but rather a question of “when” and “how fast”

Curb fossil fuel emissions – as soon as possible