NOAA/NSTA Web Seminar: The Ocean’s Role in Weather and Climate LIVE INTERACTIVE YOUR DESKTOP

The influence of the Atlantic ocean on climate, from Atlantic hurricanes to African drought Thomas L. Delworth Geophysical Fluid Dynamics Laboratory/NOAA Princeton, NJ Outline: 1.Basics of the Atlantic Ocean 2.Multidecadal changes in the Atlantic: impact on climate a.African drought b.Conditions for tropical storms c.Hemispheric temperature 3.Global warming and the Atlantic

from “Earth's Climate Past and Future”, Ruddiman. Schematic of Atlantic Ocean Circulation Ocean moves heat poleward 1.3*10 15 Watts Sinking water at high latitudes

Question: The rate of heat (energy) transported by the Atlantic ocean is ~1.3 *10 15 Watts. The amount of energy moved poleward by the Atlantic Ocean each year is the equivalent to approximately how many years of total U.S. electricity generation: 1 year 100 years 1000 years 2000 years

Observed Atlantic Sea Surface Temperature (60 o W-20 o W,6 o N-18 o N) Tropical North Atlantic Temperature (Deg C)

Outline: 1.Basics of the Atlantic Ocean 2.Multidecadal changes in the Atlantic: impact on climate a.African drought b.Conditions for tropical storms c.Hemispheric temperature 3.Global warming and the Atlantic

Atlantic Ocean Temperature (80 o W-0 o W,0 o N-60 o N)

Observed change in Sea Surface Temperature (Deg C) minus Data from Aug-Oct Where did the largest warming take place?

Tree ring records show that AMO-like fluctuations have existed for centuries. Gray et al., 2004, Geophysical Research Letters

How can we better understand (and predict) the impact of the North Atlantic ocean on climate? 1.Diagnostic analyses of observational data 2.Use computer models of the climate system to better understand how the climate system works (cause and effect) and to predict its future evolution Computer climate model is a “Virtual Earth”, in which we can perform many experiments to better understand the system.

In models, the earth’s land, ocean and atmosphere are chopped into 5 million grid cells. Horizontal Grid (Latitude-Longitude) Vertical Grid (Height or Pressure) Climate models use world’s fastest supercomputers … but need computers that are 1000 times faster (at least!).

Where is climate modeling done?

CANADA USA Princeton, NJ New York, NY Boulder, Colorado ENGLAND GERMANY JAPAN AUSTRALIA

Observed Precipitation (mm/month) 100 mm/month is about 50 inches per year Data from Univ. of East Anglia, Climatic Research Unit (CRU) Seasonal migration of Intertropical Convergence Zone (ITCZ) January July Sahel

trends in observed and simulated precipitation (JAS) Observed Simulated (Atmosphere model forced with observed SSTs )

Simulated rainfall changesModeled AMO Index Observed rainfall changes Observed AMO Index

Let’s do a poll question! The rainy season in the Sahel region of Africa is:

Simulated Summer Rainfall Changes Associated with Warm North Atlantic Units: cm/day Blue means more rainfall when the North Atlantic is warm

Simulated multidecadal JJAS surface air temperature difference (K) ( ) – ( )

Question: The Sahel region of Africa is particularly prone to drought because: It is located far from the ocean It is located in a region of sharp transition between tropical rainforests to the south and desert to the north The mountainous terrain blocks moisture from the ocean

NOAA National Hurricane Center 2005 Outlook

Reduction in Wind Shear when North Atlantic Warms relative to South Atlantic ObservationsModel (GFDL CM2.1) Red means less shear, and therefore more favorable conditions for hurricanes. CONCLUSION: Models demonstrate that a warming North Atlantic (relative to the South Atlantic) CAUSES atmospheric circulation changes that are favorable for tropical activity. Zhang and Delworth, 2006

Outline: 1.Basics of the Atlantic Ocean 2.Multidecadal changes in the Atlantic: impact on climate a.African drought b.Conditions for tropical storms c.Hemispheric temperature 3.Global warming and the Atlantic

Let’s do a poll question! If all emissions of carbon dioxide were stopped tomorrow, how long would the ocean continue to warm?

You are here (now) What the Climate Models Predict:

Observed and Modeled Tropical North Atlantic SST Modeled (GFDL CM2.1) Observed Steady or slightly cooling temps Rapid Warming Key uncertainty: Role of aerosols In late 20 th century

Looking at 21 st Century Simulations Projected Atlantic SST Change (relative to mean) Areal average 70 o W-0 o W 0 o N-60 o N Results from GFDL CM2.1 Global Climate Model (SRES A1B) Observed Trend from

Summary/Discussion - Atlantic Ocean plays a crucial role in climate through transporting large amounts of heat from the Tropics to higher latitudes. - Multidecadal fluctuations in ocean circulation have strong influence on climate, including African and Indian monsoon rainfall, Atlantic hurricane activity, and North American temperature. - Increasing greenhouse gases are significantly warming the Atlantic, and will continue to do so in the future.

National Science Teachers Association Gerry Wheeler, Executive Director Frank Owens, Associate Executive Director Conferences and Programs Al Byers, Assistant Executive Director e-Learning LIVE INTERACTIVE YOUR DESKTOP NSTA Web Seminars Flavio Mendez, Program Manager Jeff Layman, Technical Coordinator Judith Lopes, Administrative Assistant Susan Hurstcalderone, Volunteer Chat Moderator