Ocean Response to Global Warming/Global Change

1. Ocean Response to Global Warming/Global Change Possible changes in ocean circulation and how they may affect regional climate patterns William Curry Woods Hole Oceanographic Institution Environmental Defense May 12, 2005

2. Ocean Response to Global Warming/Global Change Possible changes in ocean circulation and how they may affect regional climate patterns William Curry Woods Hole Oceanographic Institution July 19, 2005

5. What is the Ocean’s Role in Climate? • the ocean covers 70% of the earth’s surface • the ocean stores a thousand times more heat than the atmosphere • seawater stores four times more heat per unit mass than air • it transports 25 to 50% of the energy received from the sun

6. What is the Ocean’s Role in Climate? • it circulates slowly, on time scales of decades to centuries • it is the major source of heat to some regions like the North Atlantic • it sets long-term patterns of atmospheric circulation affecting climate systems like ENSO, NAO

7. How will the Oceans Change as the Earth Warms? • the oceans will warm, sea level will rise • its salinity balance will be altered • its ability to absorb CO2 will change • it will impact atmospheric circulation, storm tracks, severe storms, and the frequency and distribution of droughts

8. The oceans have been warming for the last 50 years Levitus et al., 2000

9. The net warming above 3000 m is 0.06o C The oceans have absorbed about 30 times more heat than the atmosphere since 1955 Oceans 18.2 x 1022 J Atmosphere 6.6 x 1021 J Indistinguishable from the expected response to rising CO2 – an anthropogenic signal Levitus et al., 2001

10. What are the Implications? The oceans will continue to absorb heat as the climate system warms Warming will cause sea water to expand The effect of heat absorption will be to delay the warming of the atmosphere The rate and magnitude of global warming will be affected by how the ocean circulates in the future – when and where will it release the stored heat?

11. What about Salinity? • Oceans contain 97% of Earth’s water • Oceans experience 86% of evaporation • Oceans receive 78% of planetary precipitation • A 1% increase in Atlantic precipitation equals the annual Mississippi runoff • A key element of the global water cycle

12. The Water Cycle Will Accelerate With Global Warming • A warmer atmosphere will carry more water vapor, because of the exponential increase of vapor pressure with temperature. • An enhanced water cycle will change the distribution of salinity in the upper ocean.

13. Global Salinity and E-P distributions Source: R.Schmitt,WHOI Source: HydroBase2 Sea surface salinity distributions are determined in large part by E-P patterns

14. Increasing salinities in the tropical Atlantic

15. Surface Water Over the same 40-year period, salinities have been increasing.. …. a shift in the entire Atlantic hydrological cycle? Ruth Curry et al., 2003

16. Tropical Salinities Increasing for last 40 years 1967-1972 1980-1984 1995-2000 Fresher Saltier Ruth Curry (pers. comm.)

17. Summer Arctic Sea Ice 1979 2003 NASA Goddard Space Flight Center

18. Greenland is melting NY Times June 8, 2004

19. Largest effects in the upper 1000 m Curry and Mauritzen, in press

20. Freshwater storage and net flux anomalies 0.066 Sv 19000 km3 4000 km3 15000 km3 10,000 km3 Ruth Curry & Cecile Mauritzen, in press

21. Large Scale Ocean Circulation

22. Fresher Deep Water Flowing South at 3000 m 1967-1972 1980-1984 1995-2000 Fresher Saltier Ruth Curry (pers. comm.)

23. Two Important Ocean Processes will be Affected • Convection and thermohaline circulation – the large scale ocean circulation • Air-sea coupling – El Nino and the North Atlantic Oscillation

24. Large-scale Ocean Circulation Affects the Heat Transport

25. Large Scale Ocean Circulation

26. Conveyor ON

27. Conveyor OFF

28. Temperature Response • Strong cooling in North Atlantic • Warming everywhere else • No net global change Manabe and Stouffer, 1997

29. Greenhouse models predict a slowdown in the deep water circulation IPCC Report

30. Air-Sea Interactions Ocean surface temperatures set atmospheric circulation

31. El Nino 1997-1998 November 1997 January 1997 Goddard Space Flight Center - NASA

32. Goddard Space Flight Center - NASA

33. The North Atlantic Oscillation Low Phase High Phase

34. The North Atlantic Oscillation High Index Low Index Fewer hurricanes More hurricanes

35. North Atlantic Oscillation Index

36. NAO and Gulf Stream Transport

37. The Gulf Stream South of Cape Cod

38. Summary • The ocean and atmosphere work together to affect climate • Surface conditions of the ocean set atmospheric circulation – the surface conditions are changing • Deep water produced in the Atlantic is exported to the world • The circulation system is density driven – warm, salty water becomes cold, dense, salty deep water • The salinity balance appears to be changing

39. Summary • Heat released to the atmosphere by the oceans is an important source of heat to the Atlantic region • Several models of future greenhouse climate produce a significantly altered Atlantic circulation • Some of the changes predicted by the models may be occurring in the Atlantic today

40. The Ocean and Climate Change Institute Woods Hole Oceanographic Institution