Climate L2 Greenhouse gases current interglacial Last glacial

Climate L2 How warm was the last interglacial? Global ice cover is easier to reconstruct than temperature: Less glacial ice ~100,000 years ago than today –Due to reduction of polar ice sheets Temperatures warmer at least some places – coastal Pacific, Atlantic, Indian Oceans – expansion of forest into tundra in North America & Asia Image: Paleomap project

Climate L2 18,000 yrs ago: sea level ~130 m lower Image: Paleomap project

Millions of years ago, the Earth was much warmer Zachos et al., 2008

Myr: no ice sheets (well, mostly), crocodiles in Hudson Bay, lemurs in Norway, dinosaurs Image: Paleomap project

65 Myr: No more dinosaurs …as such (bird-like ones survive) Other species (mammals, plants) also extinct Why? Yucatan Peninsula: 180-km wide crater impact Could blow enough aerosols (suspended particles) to block sunlight (Climate factor #2, albedo) for years Outstanding questions: Exact timing of Yucatan asteroid? Multiple impacts? Image: NASA

Climate L2 Mass extinctions over millions of years Millions of years ago 65 Myr asteroid impact extinction 55 Myr thermal max Rates of extinction (% of species)

Climate L2 Past extinction rates are notoriously difficult to estimate "If we find a mass extinction, we have great difficulty determining whether it was a 'bad weekend' or it occurred over a decade or 10,000 years" -Charles Marshall, UC-Berkeley

56 Myr: big warming in already warm world 2,000 Gt of carbon entered atmosphere and ocean Global temp increased by more than 5ºC in <10,000 years

56 Million year agoToday Background CO 2 levels unknown, 2-10x present ~3,000 Gt C released –Maybe through methane hydrates? Little or no polar ice Tropical ocean temps ~95°F “Major extinction” of single- celled shelled oceanic plankton (forams) –Maybe because of low oxygen? CO 2 level ~400 ppm ~5,000 Gt C released by humans by 2400 Antarctica, Greenland permanent ice caps Tropical ocean temps ~84°F “Present (extinction) rates are higher than during most past mass extinctions.” - C. Marshall –1-2% loss measured so

Lessons from the past What positive feedbacks could contribute to global warming? How fast and how much does carbon dioxide raise temperatures? 55 Myr ago global temperatures suddenly (~1000s of years) warmed 5 - 9°C Triggered by carbon release ~2x?? of CO 2 "We were pretty surprised that the increase in atmospheric carbon dioxide turned out to be so small. To explain the entire warming, you would need a whole lot more carbon.” - Dr. Richard Zeebe, coauthor, “Carbon dioxide forcing alone insufficient to explain Paleocene-Eocene Thermal Maximum warming, Nature, 2009

Climate Change During Last 55 Myr Global cooling over last 55 Myr –Terrestrial records Faunal change Floral changes Evidence for glaciations –Marine records Oxygen isotopic composition of foraminifera

Climate L2 Future(s) temperature change global economic development regional economic stratification global environmental consciousness regional environmental consciousness and economies 1992 projection Source: IPCC 2001

Climate L2 Projected Pacific Northwest Temperature Changes relative to °F 3.6°F 0°F 10.8°F 14.4°F +2.2ºF ( ºF) +3.5ºF ( ºF) +5.9ºF ( ºF) °C Rate of change per decade expected to be 3x greater through mid-21 st century, data from Climate Impacts Group Choice of emissions scenario matters more after 2040s

Climate L2 How does current change compare to past? Questions – Was change local? (temperature, precipitation) – Global (climate, greenhouse gases) – Comparable to present day? (atmosphere, continents) If projections are realized of +5  C in this century, then the Earth will have warmed ~50x faster than at end of the last ice age Several degrees of global warming would be bigger than any comparable increase over the last 50 million years