climate change: from dinosaurs to the grandchildren bob marsh

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)

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:

The Last 150 years:

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”Coalbrookdale by Night”(P. de Loutherbourg, 1801)

US Interstate Highway I5, north of Los

Angeles

Late Victorian Industry

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

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 …

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:

The Last 450,000 years:

Drilling Antarctic ice cores:

& deep ocean sediment cores:

Part of the EPICA ice core Analysing a sediment core

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)

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 …

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

So why does climate change so much & in so

many different ways?

Let’s look at some causes…

Time

Time

“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

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

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

So is recent climate change natural?

… or have we influenced it?

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

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

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

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 …

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 …

… 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

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)

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

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

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

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 …

Thank You for listening!