global warming and the planetary water cycle ruth curry woods hole oceanographic institution ruth...
TRANSCRIPT
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