As the world warms: coral records of climate change Kim Cobb EAS, Georgia Inst. of Technology Acknowledgements Lab members: Intan Suci Nurhati Julien Emile-Geay Laura Zaunbrecher James Herrin Hussein Sayani EAS undergrads Chris Charles Scripps Inst of Oceanography Larry Edwards, Hai Cheng University of Minnesota with special thanks to: Norwegian Cruise Lines Palmyra Research Consortium Sarawak Department of Forestry, Malaysia NOAA, NSF

Which of the following are scientific statements? 1)Reducing CO2 emissions would hurt the economy. 2) Improved technology is the best way to slow global warming. 3) A warming of 1ºC over the next 50yrs is dangerous. 4) Global temperatures were 5ºC colder during the Last Glacial Maximum. 5) Hurricane Katrina was caused by global warming.

Which of the following are scientific statements? 1)Reducing CO2 emissions would hurt the economy. 2) Improved technology is the best way to slow global warming. 3) A warming of 1ºC over the next 50yrs is dangerous. 4) Global temperatures were 5ºC colder during the Last Glacial Maximum. 5) Hurricane Katrina was caused by global warming.

Why do % of climate scientists believe that CO 2 is warming the planet? 1.Theory predicts that increasing atmospheric CO2 should warm the planet. 2.Geologic evidence links CO2 and temperature in the past. 3.The warming is unprecedented in the most recent centuries (dwarfs natural variability). 4.Climate models show that rising CO2 is necessary to simulate 20 th century temperature trends (solar and volcanic minor players).

Ice core climate and CO 2 records tiny gas bubbles in the ice trap ancient air samples

Atmospheric CO 2 and temperature over the past 650 thousand years CO 2 and temperature are closely linked on geologic timescales #2

To understand how climate has changed in the past, we need to use records of climate preserved in ice cores, ancient tree rings, coral bands, and other “paleoclimatic” sources: key is to CALIBRATE to temperature records

The “Hockey Stick” Key Points: error bars increase as you go back in time natural variability accounts for <0.5ºC over the last millennium late 20 th century temperature trend is unprecedented #3

Intergovernmental Panel on Climate Change (IPCC) 2001 #4 Solar and volcanic only anthropogenic only natural & anthropogenic

The uncertain climate future Range of scenarios: Strict international agreements  CO2 at 600ppm by 2100*390ppm today Mid-ground  850ppm by ppm 1800 Business as usual  1550ppm by 2100 IPCC AR4, 2007

but we need to know about regional climate changes, and specifically about regional precipitation changes white = models disagree color = models mostly agree stippled = models agree IPCC AR4, 2007

Research Goal: constrain tropical Pacific response to anthropogenic global warming Approach: reconstruct tropical Pacific climate at high-resolution for the last millennium Dai and Wigley, 2000 El Niño Temperature El Niño Precipitation WHY? “El Niño-Southern Oscillation” (ENSO) ENSO is a climate pattern in the tropical Pacific which arises from coupled interactions between the atmosphere and ocean ENSO impacts global climate every 2-7 years (huge impact on rainfall) Tropical Pacific climate variability over decades to centuries to millennia poorly constrained

Tropical Pacific climate and global warming ENSO std in control run ENSO std Observed ENSO std in GHG run El Niño La Niña Collins et al., 2004 Timmermann et al., 1999 Cane et al., 1997 We don’t know how the tropical Pacific will respond to global warming, if at all. Studies are contradictory because: 1)climate data are scarce prior to )climate models do not simulate ENSO accurately more El Niño’s more La Niña-like both

Research Questions How has the tropical Pacific climate system responded to CO 2 forcing? What aspects of present tropical Pacific climate are unprecedented? compare last several decades to recent centuries Fanning 2005-? Palmyra 1997-? Christmas 1998-?

Corals: The geologic record of El Niño CORALS from the tropical Pacific record El Niño’s in the geochemistry of their skeletons Living Porites corals provide records for the last 200 years Fossil Porites corals enable us to extend the record back many centuries

Generating climate reconstructions from the Palmyra corals : 1)Recover the corals, both modern (~10) and fossil (~100). 2)Prove that the coral geochemistry tracks large-scale climate. ie. Calibrate the modern coral record against the instrumental record of climate. 3)Apply geochemistry to fossil corals and date them (U/Th dating). Aerial view of Palmyra

Modern The Palmyra Island Coral Collection Little Ice Age (LIA) canals frozen in Europe Medieval Warm Period (MWP) Greenland green

Palmyra coral oxygen isotopes vs. tropical Pacific SST

Overlapping fossil corals: ancient El Niño events Good reproducibility between coral geochemical records increases confidence in coral climate reconstructions.

A millennium-long reconstruction of tropical Pacific temperature Key climate observations: 1) late 20 th century warming is unprecedented in the last millennium 2) no cooling during the Northern Hemisphere’s “Little Ice Age” 3) significant cooling implied during the NH’s “Medieval Warm Period”

Conclusions -paleoclimate data have an important role to play in global climate research - corals provide quantitative reconstructions of temperature - evidence for ongoing tropical Pacific climate change that could shape future global temperature and precipitation patterns A climate scientist’s plea: Get your climate information from a climate scientist (not the media, politicians, etc) Use flourescent light bulbs, don’t drive SUVs, a

The Earth’s ice is melting, sea level has increased ~3 inches since 1960 ~1 inch since signs of accelerating melting are now clear -land ice particularly striking, poles more complicated -IPCC estimates project current trends forward i.e. LOWER estimate using no acceleration The uncertain sea level future

Stroeve et al, 2008

Sea level rise: IPCC says 7” to 22” by 2100, much more if rapid ice sheet collapse occurs most scientists would go on record for 1m rise (30 inches)

Projected temperature change: global view Take-homes: -poles warm more -land warms more -ocean warming patchy and complex uneven warming will shift rainfall patterns

Diffenbaugh et al, 2005 US Regional models use global model output, run at high-resolution (5km) grid Length of heat waves increase (# days/event) Peak temperatures increase

white = models disagree color = models mostly agree stippled = models agree Projecting precipitation is VERY uncertain business, yet extremely critical to human impacts. Projected precipitation change: global view

Projected precipitation change: regional view change in yearly average precipitation # heavy rain days # dry days Diffenbaugh et al, 2005 mm/daydays/yr

IPCC says increase in hurricane intensity “likely” (66%)

CERTAIN UNCERTAIN Warming of 1-6°C by Sea levels will rise by 6 to 30 inches by Precipitation patterns will change. More erratic precipitation. Extreme events will increase, hurricanes more intense. Prospect of abrupt climate change.

What is a country to do? There are only three (prudent) options: 1)use less energy - drive less, drive smaller (plug-in?) cars - conserve electricity - recycle, reuse 2) make “clean” energy - solar power, wind power, nuclear energy 3) take CO2 out of the sky (much more difficult) …. but how much at what cost?

Some clear lessons: 1)efficiency makes $$ 2)gains from cellulosic biofuels likely (not corn ethanol!) 3) taking CO2 out of the sky is more costly than not putting it in the atmosphere to begin with

My homepage: Scientific Summary Strong evidence supports the idea that anthropogenic CO 2 is warming the planet. Future climate changes in a warming environment are still uncertain, although: -sea level rise certain (but how much by when?, ~1m starting point) - SE precipitation will become more erratic (water resource management) -prospect for increasing hurricane activity A Climate Scientist’s Plea Evaluate the scientific evidence for yourselves, from a scientific source. Distinguish between the science of global warming and the politics/economics of global warming.