1.2 Climate change: urgency in slow motion (B.Verheggen)

Climate Change: Urgency in Slow Motion

Bart Verheggen, PhD Amsterdam University College

Climate Communication & Consultancy http://KlimaatVerandering.wordpress.com/ http://OurChangingClimate.wordpress.com/

@KlimaatVeranda @BVerheggen

The scientific position

“studies from diverse sources indicate a consensus that climate changes will result from man’s combustion of fossil fuels and changes in land use.”

National Academy of Sciences Archives, An Evaluation of the Evidence

for CO2-Induced Climate Change, 1979

IPCC was established in 1988 in response to scientific predictions

has hardly changed since 3 decades…

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Arrhenius, Fourier, Tyndall, …

Scientific process

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• Science is based on critically evaluating available evidence in the context of existing knowledge

• If more knowledge confirms the existing theory • This leads to a growing consensus amongst

scientists about the big picture

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Greenhouse effect

Greenhouse gases absorb infrared radiation

Less energy escapes to space

Earth is warmer than it would otherwise be

Human activity has increased the concentration of greenhouse gases

Earth retains more energy and heats up as a result

Observations (from space and from earth’s surface) confirm the enhanced

greenhouse effect

Bart Verheggen

http://svs.gsfc.nasa.gov/vis/a000000/a004000/a004030/

Global warming since 1880 (5 year running mean)

Long term trend vs short term variability

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http://sks.to/escalator

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The increase in Earth’s total heat content is dominated by the ocean

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Climate has always changed

Process • Plate tectonics • Orbital variations • Carbon cycle • Sun • Volcanoes • El Niño / La Niña

• Man-made GHG & aerosols

Timescale (years) > 1,000,000 > 10,000 (ice ages) 1000 – 1,000,000 variable 1-3 1-2 variable

Solar output varied strongly past 400 years

Little Ice Age

But no trend since 1950’s

• No trend in the sun (or cosmic rays) since 50 years

• Nights have warmed more than days • Stratosphere has cooled • Enhanced greenhouse effect observed from

space and from the ground

Inconsistent with dominant solar influence

Sun or Greenhouse Gases?

• No trend in the sun (or cosmic rays) since 50 years

• Nights have warmed more than days • Stratosphere has cooled • Enhanced greenhouse effect observed from

space and from the ground

“fingerprint” of enhanced greenhouse effect

Sun or Greenhouse Gases?

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Bart Verheggen

Observations in black Model simulations in color

Projections of future climate change

If global emissions peak within next few years then decline

Ongoing increases in global greenhouse gas emissions

Emissions cuts make little difference for next few decades (inertia)

Expected warming in the future depends on: - total emissions (e.g. red or blue trajectory) - climate system response (uncertainty band)

Con

cent

ratio

n (p

pm)

Year

Em

issi

on (G

ton

/ yea

r)

emission

concentration

Decreasing the CO2 concentration takes much longer than

increasing it

Long term sea level rise

Sea

leve

l ris

e (m

etre

s)

Climate responds very slowly to emission reduction

• Oceans act as heat buffer • Long response time of CO2

– Increasing CO2 goes faster than decreasing CO2 – Climate warming goes faster than climate cooling

• Sea level responds even slower than temperature

Climate responds very slowly to emission reduction

Urgent?

• Warming is delayed

• Cooling will be delayed much more so

• Thus early action is needed (*)

(*) assuming we value having a relatively stable climate

• Direction of changes is clear

- Earth is warming up

- It’s due to us

• Uncertainty about speed

• Delayed response

“if you jump out of an airplane you need a crude parachute more than an accurate altimeter” (Herman Daly)

Conclusions

“What’s the use of having developed a science well enough to make predictions if, in the end, all we’re willing to do is stand around and wait for them to come true?”

Sherwood Rowland

Thank you!

http://KlimaatVerandering.wordpress.com/ http://OurChangingClimate.wordpress.com/

@KlimaatVeranda @BVerheggen