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Anthropogenic Climate Change: Past, Present, and Future

Dr. David KaroweDepartment of Biological Sciences

Earth’s climate is always changing

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- air bubbles trapped in ice reveal past CO2 levels

Antarctic ice cores provide a record of Earth’s climate over the past 800,000 years

Over the past 800,000 years, Earth has experienced repeated ~100,000 yr climate cycles

- greenhouse gasses have co-varied with temperature

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Pleistocene climate cycles are due to Milankovitch Cycles

Last Glacial Maximum was about 18,000 years ago

- global temperature was only about 5o C cooler than today

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and sea level was about 350 feet lower

Tree ring and thermometer records indicate two anomalous periods since 500 AD

Little Ice Age

modern warming

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Video included here

see 18,000 bp – present at

http://homepages.wmich.edu/~karowe/Teaching%202010.html

Animation: North America 19,000 BC to 3,000 AD

“Little Ice Age” from ~1500-1800 AD

- global temperature was ~ 1o C cooler than today - most of Europe was noticeably cooler

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Little Ice Age was due to decreased solar activity during the Maunder Minimum

Tree ring and thermometer records indicate two anomalous periods since 500 AD

Little Ice Age

modern warming

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Climate change since the Industrial Revolution

12 warmest years in history: 2002-2012, 1998*

Warmest year: 2010

Since 1900, Earth has warmed ~ 0.8o C

- warming is now 20x faster than any time in ice cores

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Temperature difference relative to 1950-1980

video available at http://data.giss.nasa.gov/gistemp/animations/

- severe rainstorms have become more common

- 20% increase in Michigan since 1948

- 50% increase in southwest Michigan

Precipitation is a very important component of climate

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Flooding has increased globally in the last 50 years

1950-1959

2000-2009

Much of the world is also already experiencing more frequent and stronger droughts

Palmer Drought Severity Index (PDSI)

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Arctic summer sea ice has been decreasing rapidly

- record low in 2012

August 27, 2012

Greenland ice sheets is melting at an accelerating rate

- meltwater lubricates underside ofice sheet

2012

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Major climate predictions are already coming true in the U.S.

- in 2011, 10 states had their wettest spring on record

As a result, there was extensive flooding

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2012 was the warmest year on record for 19 states- and for the entire contiguous U.S.

December 2012

74% drought

This year, severe drought covered much of the U.S.

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Can climate change be due to “natural variation”?

- three lines of evidence argue that current climate change is NOT due to natural factors

1. Since 1900, heat added by greenhouse gassesis about 20 times heat added by the sun

heat added by greenhouse gasses

heat added by the sun

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2. While Earth has been warming fastest, energy from the sun has decreased

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3. Models do a good job of replicating past climate change only if they include anthropogenic factors

- natural factors would have caused a slight coolingsince 1900

anthropogenic and natural factors

natural factors only

observedmodeled

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In two major ways, current warming is very different than any warming period

in at least the last 800,000 years

1. It’s at least 20 times faster

2. It’s happening while solar input is decreasing

But, since climate has changed before, it must be changing now for the same reason, right?

Would the same reasoning apply to recent increases in forest fires and lung cancer?

Best estimate: at least 95% of current warming is due to human activities

DeforestationGreenhouse gas emissions

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What does the future hold?

It depends on the choices we make

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4o

Depending on our actions, Earth is likely to warm by at least 2-4o C by 2100

“Business as usual”

Alternate energy sources

Zero emissions

0.6o

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Will a 4o temperature rise matter?When Earth was 5o cooler:

Arctic is likely to warm at about twice the global rate

- Arctic is site of strongest positive feedbacks

e.g. with 3.5o C average global warming by 2100:

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Arctic summer sea ice expected to disappear by 2070

For the video include here, see present – 1,000 years into the future at:

http://homepages.wmich.edu/~karowe/Teaching%202010.html

Animation: North America 19,000 BC to 3,000 AD

Many glaciers are likely to disappear by 2100, including all intertropical glaciers by 2030

- 750,000,000 people in China and India rely on glaciersand seasonal snowpacks for their water supply

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Continued loss of ice sheets

- full melting of Greenland ice sheet →

- full melting of Antarctic ice sheet →

7 m sea level rise

57 m sea level rise

Sea level is expected to rise by 1-2 meters by 2100

- 10 million to 300 million people could be flooded eachyear with 1 meter rise

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Much of U.S. would be affected by 1 meter rise

Increase in inland flooding due to severe rainfall

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Decrease in summer rainfall throughout the U.S.

2060-2069

Much of the world is likely to experience much more frequent and stronger droughts by the 2060s

Palmer Drought Severity Index (PDSI)

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- current drought indices may no longer work properly

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Michigan will experience many more days over 90o F

Most summers are likely to be hotter than any experienced thus far

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Low Moderate High

Probability of disappearing climate

Many areas are also predicted to experience “disappearing climates” by 2100

Bottom Line:

1. We’re causing climate to change at an alarming rate

2. If we continue on our current path, the future is very likely to include unprecedented hardships for all of Earth’s species, includinghumans

3. Many of the worst scenarios can be avoided by choices we have available today