Climate Variability and Change: Basic Concepts€¦ · • Global Plate Tectonics • Sunspots •...
Transcript of Climate Variability and Change: Basic Concepts€¦ · • Global Plate Tectonics • Sunspots •...
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Climate Variability and Change: Basic Concepts
Jeffrey A. AndresenDept. of Geography
Michigan State University
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Weather versus Climate
• The American Meteorological Society’s Glossary of Meteorology defines climateas:“The slowly varying aspects of the atmosphere–hydrosphere–land surface system”
• Weather describes the same thing but on relatively short time scales (e.g. hours or days)
• ‘Climate is what we expect, weather is what we get…’
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Some Notable Pre-Instrumental Trendsin the Great Lakes Region
• Tropical humid conditions during the Carboniferous and Devonian eras.
• Frigid, glacial/periglacial conditions as recently as 12,000 years ago during the end of the Pleistocene era.
• During early portions of the Holocene era, climate in the region warmed rapidly, resulting in a relatively mild and dry climate which lasted until about 5,000 YBP. Great Lakes levels fell until the lakes became terminal or confined about 7,900 YBP and vegetation in the region gradually transitioned from boreal to xeric species.
• Beginning about 5,000 YBP, climate cooled and precipitation totals increased, favoring the establishment of more mesic vegetation.
• During the late Holocene, the region experienced a period of relatively mild temperatures from approximately 800A.D. to 1300 A.D. followed by a period of relatively cool temperatures from about 1400A.D. until the late 19th Century.
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The Earth’s climate system is dynamic: It changes. It always has and it always will.
• So why are we concerned now?1. We might be responsible.2. We might not like the changes.
• The globe is projected to warm 1.0-4.0°C by 2100.– Is that a big deal?– Depths of the Ice Ages
• 5-6°C colder than today.
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‘Natural’ Mechanisms and Processes Leading to Climate Change:
• Global Plate Tectonics• Sunspots• Variations in Earth orbit (Milankovitch Theory)• Vulcanism (e.g. Mt. Pinatubo 1991)• Meteor Impact (e.g. Chicxulub, K-T extinction
65M ybp)• Periodic changes in the earth’s carbon, nitrogen
cycles
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Anthropogenic Mechanisms and Processes Leading to Climate Change:
• Changes in atmospheric greenhouse gas concentrations
• Changes in other atmospheric gas concentrations (e.g. ozone depletion)
• Land use changes
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Mean global temperatures have increasedapprox. 0.9°C during the past century
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How can the Earth physically warm up over time?
• At its simplest, long term warming of the earth’s surface boils down to three possibilities.
• The Earth will warm if:– The Sun gets brighter– The Earth gets darker (less reflective)– The Earth cannot reradiate heat fast
enough
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Has the Sun been getting brighter?• In short, no.• During the last 35 years the solar ‘constant’
has decreased.• Solar cycle 24
is now beginning so we should experience roughly 0.24 W/m2
heating by 2013
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Has the Earth been getting darker?
• No. If anything, it has been brighter/more reflective.
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Process of elimination means…
• Something must be keeping energy (heat) from escaping like it previously did.
• That ‘something’ is the set of greenhouse gases, which include:– Carbon dioxide– Methane– Halocarbons– Ozone – Nitrous oxide
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*** For reference, the amount of solar energy absorbed at the top of the atmosphere averaged globally is 240 W/m2.
Concentrations of GHGs in the atmosphere are increasing…
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…and have been strongly correlated withtemperature changesin the past.
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Historical Climatic Trends:Instrumental Record
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Mean Temperatures vs. Year, Michigan1895-2010
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Mean Winter Temperatures vs. YearIronwood, MI
1902-200
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Great Lakes Region (32°F threshold)
-10
-5
0
5
10
1895 1915 1935 1955 1975 1995
Year
Fros
t-Fre
e Se
ason
(day
s fro
m n
orm
al)
Length Spring FallSource: K. Kunkel, Midwest. Reg. Clim. Center
Changes in the Length of the Frost Free SeasonGreat Lakes Region
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Annual Precipitation vs. Year, Michigan1895-2010
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Hydrologic Variables vs. YearOwosso, MI 1900-2009
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Impacts of Climatic Variability
Past history suggests that society may be able to cope/adapt with steady climatic changes, but possibly not with changes in variability
(e.g. changes in extremes, storminess)
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(Source: NCDC, 2011)
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Projecting the Future: Global Climate Models (GCMs)
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Natural Variability or Anthropogenic Signal?
(Source: IPCC, 2007)
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Source: (IPCC, 2007)
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Model-Projected Mean Temperature DifferencesPontiac, MI 1990-2099
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Model-Projected Precipitation RatiosPontiac, MI 1990-2099
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Projected Temperature Changes
Hayhoe et al (2010)
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Strategies
• Adaptation (learn to cope, adapt)– New technology– Migration, Abandonment (‘habitat tracking’)
• Mitigation (reduce or solve problem)– Collection/Storage of carbon
• Anthropogenic• Biological
– Geoengineering
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Summary• Overall, mean average temperatures in Michigan
rose approximately 1.0ºF during the past century. Warming of about 2.0ºF has occurred between 1980 and the present, much of it concentrated during the winter season and at night.
• Milder winter temperatures have led to less ice cover on the Great Lakes and the seasonal spring warm-up is occurring earlier than in the past.
• Annual precipitation rates increased from the 1930’s through the 1990’s but have leveled off recently.
• Most recent GCM simulations of the Great Lakes region suggest a warmer and wetter climate in the distant future, with much of the additional precipitation coming during the cold season months.
• Projections of future climate change in Michigan suggest a mix of beneficial and adverse impacts.
• A changing climate leads to many potential challenges for dependent human and natural systems, especially with respect to climate variability.
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Questions?
Michigan State University
Questions?