Climate Change: From Dinosaurs to the Grandchildren Bob Marsh.
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Transcript of Climate Change: From Dinosaurs to the Grandchildren Bob Marsh.
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Climate Change: From Dinosaurs to the Grandchildren
Bob Marsh
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Climate changes …
… on all timescales …
increasingly rare snow on Beachy Head (27/12/05)
Chalk strata - laid down in warm shallow seas (89-93 million years ago)
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The Last 25 years:
El Niño (December 1997)
La Niña (December 2000)
Arizona floods
(El Niño,82/83)
Yellowstone fires
(La Niña, 88)Pinatubo erupts (1991)
Tanzania drought
(recent El Niño)
Pacific Sea Surface Temperature
Changes:
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The Last 150 years:
?
”Coalbrookdale by Night”(P. de Loutherbourg, 1801)
US Interstate Highway I5, north of Los
Angeles
Late Victorian Industry
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The Last 2000 years:
“Dark Ages” (600-1000 AD) triggered by major volcanic eruption in 535 AD? Good Medieval Harvests “Scene on the Ice” (H. Avercamp, c. 1600)
From tree rings …… to modern observations
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The Last 12,000 years:“The Seven Wonders of the World”
(spanning 2650 - 247 BC)
“Green Sahara”& Middle East
helps…
Precipitation change, 6500 BC
… rise of agriculture & civilization in the “Fertile Crescent”
(9000-7000 BC), leading to …
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The Last 50,000 years:Retreat of the North American ice
sheet, 18,000-8,000 years ago:
Ice Age Megafauna, now extinct:
Irish ElkWooly Mammoth
Retreat of ice sheets and sea ice in the Atlantic/European sector:
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The Last 450,000 years:
Drilling Antarctic ice cores:
& deep ocean sediment cores:
Part of the EPICA ice core Analysing a sediment core
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The Last 5,500,000 years:
“Messinian salinity crisis”(Mediterranean Sea almost dries up, c. 6 Ma)
Early humans disperse from Africa (0.5-1.9 million yrs ago)
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The Last 65,000,000 years:
Dinosaur extinction linked to asteroid impact & climate changes (c. 65 Ma)
India drifts north, collides with Tibet, Himalayas built, climate changes …
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The Last 540,000,000 years:
Carboniferous Forest (c. 300 Ma)
Cambrian Ocean Life(c. 500 Ma)
Early PaleoceneForest (c. 60 Ma)
Late Carboniferous World(306 Ma) - a COLD world
Late Cretaceous World(94 Ma) - a HOT world
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So why does climate change so much & in so
many different ways?
Let’s look at some causes…
Time
Time
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“Astronomical Changes”- in Earth’s orbit around the Sun- in the tilt & wobble of our axis
• Caused glacial cycles over the last million years• Ice Ages principally a response to changes in orbit/axis• Amplified through “positive feedbacks”, changing ice sheets, vegetation & CO2
Earth’s tilt & the seasons
Earth’s orbit around the Sun
Earth’s tilt & the seasons
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Recent changes in the Sun (“Solar Irradiance”)
• Modern observations confirm that Solar Irradiance varies with the no. of sunspots
• The Little Ice Age in Europe coincided with the “Maunder Minimum” of sunspots
• Some (not much) recent global warming due to recent increase in Solar Irradiance
Sunspots seen in visible light (left) & ultraviolet light (right) light
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CO2 variations: recent & past
Past 50 years: Past 400,000 years:
• directly measured in air sampled in clean places• steadily rising, rate accelerated recently
• measured in air trapped in ice cores• follows glacial cycles
Earth has a natural carbon cycle which humans are altering
Earth’s climate is sensitive to CO2 due to the Greenhouse Effect
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So is recent climate change natural?
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… or have we influenced it?
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Big changes indeed seem underway - best seen in recent changes of ice sheets & glaciers
collapse of the Larsen BIce Sheet (West Antarctica)in February 2002
rapid retreat Alaskan glaciers
over the last 60 years
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So what about the Next 100 years?
• from IPCC 4th Assessment “Summary for Policymakers” (February 2007)• range of warming (1.1 to 6.4°C warming) due to range of emissions policy
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Future “global” warming varies much by region:
• from IPCC 4th Assessment “Summary for Policymakers” (February 2007)• land warms much more than ocean, most dramatically towards North Pole
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But despite increasingly certain predictions of climate
change over 21st century, due to human activities …
… we still struggle to forecast the details because of less
predictable natural factors …
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North Atlantic Surface Pressure: Midnight Sun/Mon
Weather forecasts for several days ahead are now highly accurate
e.g., last Monday’s big storm in the south …
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… came with a reliable 2-day warning
Same pattern forecast 2 days beforehand
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1200 Mon0100 Sun 2100 Sun 0300 Mon
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1100 Sun
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But looking further ahead, seasonal climate forecasts are often quite wrong!
e.g., Summer 2007 rainfall forecast (2 months ahead)
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- expected average rainfall in most of the UK- was actually much wetter in the midlands/south
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Although temperature is easier to forecast …
Summer 2008 “early” forecast:
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- extensive coolness expected in tropics (La Niña)- but expect a warm summer in UK, like 2003?
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Role of the World Ocean in Climate Change
• Total Ocean Net Heating = 84% of Total Earth System Warming over 1955-1998
• Absorbs about 25% of human emissions of CO2 over the last 150 years (mainly in North Atlantic & Southern Ocean) 1955-2003 linear trend in Ocean Heat Content
(Levitus et al. 2005)
Warming of upper 750m, 1993-2003(Jim Hansen, NASA/GISS)
Anthropogenic CO2 in the World Ocean(Sabine et al. 2004)
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Role of the Ocean in Recent Climate Extremes
Atlantic surface temperature anomalies August 2003relative to August average over 1985-2003
• Pattern is a combination of Global Warming & slowly-changing natural cycle in the Atlantic (recently warm)
• Such regional warming partly responsible for recent heatwaves (e.g., Summer 2003 in the UK)
European heatwave, 2003
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Global & Local Sea-Level Rise: latest measurements from space
• Satellites have provided accurate global coverage since 1992• Rate of global-mean sea-level rise recently about 3 mm per year• But lots of local variations, with fastest rises in the west Pacific & North Atlantic
TOPEX/Poseiden satellite(launched 1992)
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Geographic variations in sea-level rise over 1993-2005 (updated from Cazenave & Nerem 2004)
Changes in global-mean sea-level rise since 1992
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Role of the Ocean Circulation
• The World Ocean is connected by a global “Conveyor Belt” circulation• Helps carry heat, salt, carbon (plus bottles & ducks) around our planet
• The Conveyor Belt seems to have changed rapidly in the past, and may do so again in the future as CO2 levels rise
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What NOCS is doing about climate change- to observe & understand what is happening
“Argo” floats measuring the oceans (since 1999)RRS Discovery
RRS James Cook
We deploy Argo floats from our research ships:
- Contributing to an international effort to populate the World Ocean with Argo floats
- Monitoring oceanic changes in heat and freshwater associated with climate change
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Summary Our Climate …varies from seasons to eons, from gardens to globesometimes abruptly (and a lot!) through changes in the Sun, Earth (orbit/spin),
volcanoes, vegetation, atmospheric gases … is hard to confidently forecast, even a season aheadbut is almost certainly being changed by us …
The Oceans play a major part in climate and climate change …
by absorbing excess heatby absorbing excess CO2 (and acidifying …)by dominating longer-term variations (e.g. El Niño)by dominating particular regions, especially ours …
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Thank You for listening!