Chapter 13: Climate Change and the causes of change

OUTLINES 1. Climate and Climate System 1.1 Weather versus Climate 1.2 Climatic Controls 1.3 Climate System Components 2. Forcing, Response, Coupling and Feedback 3. Climate Change Through Time 4. Causes of Change 5. Global Warming and Greenhouse Effects 6. Climate Modeling 4.1 Coupled Ocean-Atmosphere-Land-Ice Model 4.2 Role of Forcing Factors Natural [volcanos + sun] Variability versus Human [GHG + sulfate] Effects 7. Summary

1.1 Weather versus Climate The condition of atmosphere at a given time and place Short-term (and large) fluctuations that arise from internal instabilities of the atmosphere Occurs as a wide variety of phenomena that we often experience Effects are immediately felt Social and economic impacts are great but are usually localized Many such phenomena occur as part of larger-scale organized systems Governed by non-linear chaotic dynamics; not predictable deterministically beyond a week or two.

1.1 Weather versus Climate Climate Defined as the average state of the atmosphere over a finite time period and over a geographic region (space). Can be thought of as the “prevailing” weather, which includes the mean but also the range of variations Intimate link between weather and climate provides a basis for understanding how weather events might change under a changing climate Climate is what you expect and weather is what you get. Climate tells what clothes to buy, but weather tells you what clothes to wear.

Weather and Climate

1.2 Climatic Controls The world's many climates are controlled by the same factors as affecting weather, intensity of sunshine and its variation with latitude, distribution of land and water, ocean temperature and currents, mountain barriers, land cover, atmospheric composition. This map shows sea-level temperatures (°F).

1.3 The Climate System Components

1.3 Climate System Components Atmosphere Fastest changing and most responsive component Previously considered the only “changing” component Ocean The other fluid component covering ~70% of the surface Plays a central role through its motions and heat capacity Interacts with the atmosphere on days to thousands of years Cryosphere Includes land snow, sea ice, ice sheets, and mountain glaciers Largest reservoir of fresh water High reflectivity and low thermal conductivity Land and its biomass Slowly changing extent and position of continents Faster changing characteristics of lakes, streams, soil moisture and vegetation Human interaction agriculture, urbanization, industry, pollution, etc.

2. Climate: Forcing and Response Input Machine Output

Forcing and Response: A Bunsen Burner Experiment Three major kinds of climate forcing in nature: Tectonic processes Earth-orbital changes Changes in Sun’s strength Anthropogenic forcing Urbanization Deforestation Burning fossil fuels Agriculture Response time depends on “materials” or “components”.

Response Times of Various Climate System Components

Climate System Coupling of components Positive coupling between A & B (A  B): A incr. => B incr.; A decr. => B decr. Negative coupling: A —o B A incr. => B. decr.; A decr. => B incr.

Feedbacks A feedback is a mechanism whereby an initial change in a process will tend to either reinforce the change (positive feedback) or weaken the change (negative feedback).

(+) A’s body T B’s body T A’s blanket T B’s blanket T Correct setup (–) Incorrect setup A’s body T A’s blanket T B’s blanket T B’s body T (+)

Equilibrium states Correct elec. blanket setup with negative feedback loop => equilibrium state. Stable equilibrium: Minor perturbation from this state will return to the same equilibrium. Stable eq. state Stable eq. state

Unstable equilibrium states At an unstable equilibrium state, the smallest disturbance moves the system away towards a stable equil. state (if one exists). System rarely stays at an unstable equil. state for long.

Example of a positive feedback Think about the polar regions:

Example of a positive feedback More energy retained in system Albedo decreases, Less solar energy reflected Warm temperatures Ice and snow melt If this were the only mechanism acting, we’d get a runaway temperature increase

Snow and ice albedo feedbacks in the polar regions are to blame for the large changes already observed. 1997 2000 Ninnis Glacier Tongue Antarctica

Example of a negative feedback More energy retained in system Albedo decreases Less solar energy reflected Warm temperatures More evaporation More clouds

Example of a negative feedback More energy retained in system Albedo increases More solar energy reflected Warm temperatures More evaporation More clouds

3. Climate Change Through Time

Holland in 1565 (Little Ice Age)

Climate Change Since the Last Glacial Maximum Data important for estimating past climate include: lake bottom sediment, ice cores, fossil evidence, written documents, coral isotopes, calcium carbonate layers in caves, borehole temperature, and dendrochronology or tree ring data. These data have helped identify several important climate change events in the past 18,000 years.

The Earth’s Climate History Over the last century, the earth’s surface temperature has increased by about 0.75°C (about 1.35°F). Little Ice Age = Cooling during 1,400 A.D. – 1,900 A.D. (N.H. temperature was lower by 0.5°C, alpine glaciers increased; few sunspots, low solar output) Medieval Climate Optimum (Warm Period) = Warming during 1,000 A.D. – 1,300 A.D. in Europe and the high-latitudes of North Atlantic (N.H. warm and dry, Nordic people or Vikings colonized Iceland & Greenland) Holocene Maximum = 5,000-6,000 ya (years ago) (1°C warmer than now, warmest of the current interglacial period) Younger-Dryas Event = 12,000 ya (sudden drop in temperature and portions of N.H. reverted back to glacial conditions) Last Glacial Maximum = 21,000 ya (maximum North American continental glaciers, lower sea level exposed Bering land bridge allowing human migration from Asia to North America) We are presently living in a long-term Icehouse climate period, which is comprised of shorter-term glacial (e.g., 21,000 ya) and interglacial (e.g., today) periods. There were four periods of Icehouse prior to the current one. For most of the earth’s history, the climate was much warmer than today.

Proxy Records of Climate Recent times: instrumental More recent times: historical, tree rings, ice cores Proxies for more ancient climates are found in sediments or inferred from fossils and land forms. Limted to usually last 500-1000 years except for ice cores Can generally only resolve changes that occur over 100 years or greater

Yearly Temperature Change for the Last 1000 Years Small climate changes (0.5°C) Data from tree rings, corals, ice cores, and historical records are shown in blue. Data from thermometers are shown in red. About 1000 y.a., the N.H. was cooler than now (e.g., 1961-1990 average). Certain regions were warmer than others. Warm and dry summers in England (1000-1300): vineyards flourished and wine was produced. Vikings colonized Iceland and Greenland.

Global temperature over the last 1000 years. Global temperature over the past 1000 years. The past 140 years Global temperature over the last 1000 years. Going back further in time, looking at the past 1000 years, we cna see that average temperatures are higher now than they have been in the past 1000 years. CO2 is also higher now than in the past 1000 years.

Yearly Temperature Change for the Last 140 Years Data over the globe (land and sea). Warming periods: 1900-1945 (by 0.5°C), the mid-1970s to present. The warmest decade: the 1990s. The warmest year: 1998. 2001 second warmest year on record. Over last 25 years warming ~ 0.5 C Over past century warming ~ 0.75 C Cooling periods: 1945-1975.

Surface air temperature trends over the past century The warming has been greatest at night over land in the mid-to-high latitudes of the northern hemisphere. The warming during the northern winter and spring has been stronger than at other seasons. In some areas, primarily over continents, the warming has been several times greater than the global average. In a few areas, temperatures have actually cooled, e.g., over the southern Mississippi Valley in North America. www.gcrio.org/ipcc/qa/02.html

local temp. trends

An increasing body of observations gives a collective picture of a warming world and other changes in the climate system Global mean surface temperature increase (NH, SH, land, ocean) Melting of glaciers, sea ice retreat and thinning Rise of sea levels Decrease in snow cover Decrease in duration of lake and river ice Increased water vapor, precipitation and intensity of precipitation over the NH Less extreme low temperatures, more extreme high temperatures

Recent Range Shifts due to Warming Species Affected Location Observed Changes Arctic shrubs Alaska Expansion into shrub-free areas 39 butterfly spp. NA, Europe Northward shift up to 200 km in 27 yrs. Lowland birds Costa Rica Advancing to higher elevations 12 bird species Britain 19 km northward average range extension Red & Arctic Fox Canada Red fox replacing Arctic fox Treeline Europe, NZ Advancing to higher altitude Plants & invertebrates Antarctica Distribution changes Zooplankton, fish & invertebrates California, N. Atlantic Increasing abundance of warm water spp. Walther et al., Ecological responses to recent climate change, Nature 416:389 (2002)

Modes of Climate Variation Periodic variation Abrupt shift in climate state Will show proxydata and model results Warming or cooling to new climate state Changes in amplitude or frequency of climate oscillations

4. Mechanisms of Climate Variability and Change: External versus Internal Forcing Changes in the Sun and its output, the Earth’s rotation rate, Sun-Earth geometry, and the slowly changing orbit Changes in the physical make up of the Earth system, including the distribution of land and ocean, geographic features of the land, ocean bottom topography, and ocean basin configurations Changes in the basic composition of the atmosphere and ocean from natural (e.g., volcanoes) or human activities Internal High frequency forcing of the slow components by the more rapidly varying atmosphere Slow variations internal to the components Coupled variations: Interactions between the components

Factors that influence the Earth's climate

The Milankovitch Hypothesis Milutin Milankovitch first proposed the following idea in the 1930s. Changes in climatic cycles of glacial-interglacial periods were initiated by variations in the Earth’s orbital parameters (Earth-Sun geometry factors)

Eccentricity: Earth’s orbit around the sun Orbit = Ellipse (Eccentricity = 0.05 shown 0.0167 today 0.0605 maximum) Orbit = Circle (Eccentricity = 0) Varies from near circle to ellipse with a period of 100,000 years Distance to Sun changes  insolation changes

Obliquity: Tilt of the Earth’s rotational axis Cycle of ~ 41,000 years Varies from 22.2 to 24.5° (The current axial tilt is 23.5°) Greater tilt = more intense seasons If Earth’s orbit were circular, No tilt = no seasons 90° tilt = largest seasonal differences at the poles (6 mon. darkness, 6 mon. overhead sun)

Precession: positions of solstices and equinoxes in the eccentric orbit slowly change Wobbling of the axis Turning of the ellipse Period of about 23,000 years

Earth’s Orbit Changes Through Time

Warming from the last glacial interval to the present was interrupted by several large and abrupt plunges back into cold periods. Evidence points the oceanic thermohaline conveyor belt as the mechanism for these rapid climate changes

Climate Change and Variations in Solar Output More sunspots, stronger solar emissions from the Sun.

Sunspot History from Telescopes The telescope records show: 11-year sunspot cycle.

5. Global Warming and Greenhouse Effects

Natural or Anthropogenic?

Atmospheric CO2 Concentrations Are Increasing as a Result of of Human Emissions CO2 levels in the atmosphere have increased from 280 parts per million in 1860, the beginning of the Industrial Revolution, to 370 parts per million in 1998, about a 30% increase. CO2 concentration data from before 1958 are from ice core measurements (tiny air bubbles trapped in ice core samples) taken in Antarctica. Since 1957, scientists have been making continual measurements of atmospheric CO2 at an observatory in Mauna Loa, HI. [Annual variation is due to CO2 uptake by growing plants; the uptake is highest in the northern hemisphere springtime.] Over the same time period (from 1860 to present), methane concentrations have almost tripled and nitrous oxide concentrations have risen by about 15%. Greenhouse gases hang around in the atmosphere for long time periods before they are broken down. Increases in all of these gases in the atmosphere last from decades to centuries, so yesterday’s emissions are today’s visible impacts on the climate. Today’s emissions will be affecting the climate well beyond the 21st century. This is also known as our "commitment to climate change". That is, we are committed to a course of changing climate, even if we were to stop all CO2 emissions immediately, because of the long lag time of effects in the atmosphere.

Atmospheric CO2 concentrations--past 1000 years.

Global average temperatures are increasing with increases in CO2. Global Average Temperature Is Increasing The term global warming is used to describe the enhanced greenhouse effect resulting from human activities. The blue line shows CO2 records from ice cores, the tan line shows CO2 records from atmospheric measurements in Hawaii, and the red line shows mean yearly temperature trends. This steady increase of CO2 in the atmosphere has caused greater retention of heat and a gradual warming of the earth: global average surface temperature has risen by about 1°F over the last century. Temperature Trends in the U.S. Data from climate stations across the U.S.A. show that most regions of the country have warmed over the past 100 years. Trend analysis shows that temperatures have warmed between 1.8 and 5.4°F (1–3°C) over much of the U.S. A. Rainfall patterns have also changed across the U.S.A. Over, there has been an increase in precipitation events (rain and snow), and precipitation is coming down in fewer, more extreme events (floods and very heavy snowfalls).

CO2 (ppm) CH4 (ppb) 1000 2000 N2O (ppb)

6. Climate Modeling

Climate models Use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice. Climate models are mainly used for predictions and simulations.

Dynamical/physical models Using physical principles to describe the relationship among different components of climate system in the form of mathematical equations. These mathematical equations are called dynamical models. By solving the equations, we can simulate and predict the components of the earth climate system.

Climate Model – what does it do? Starts with known physical laws – conservation of momentum, energy, & mass. Views atmosphere, oceans, land as a continuum (i.e. all spatial scales present satisfying same laws). Find and uses numerical approximations to the continuum physical laws. Integrate in time to develop climate statistics same as observed-evaluate success by extent of agreement. On global scale, this agenda very successful.

Climate Model Scaling/parameterization Need to describe details within the grid boxes

Global climate model These models are the most complex. The models divide atmosphere or ocean into a horizontal grid with a typical resolution of 2-4 degree latitude by 2-4 degree longitude and 10-20 layers in the vertical. They directly simulate winds, ocean currents and many other processes. Feedback processes are simulated in the coupled atmosphere and ocean GCMs - water vapor, clouds, seasonal snow and ice.

Scheme of a coupled atmosphere ocean model and supplementary models.

Ideal gas

Newton's law

Navier Stokes Equations

Coriolis force

First law of thermodynamics

Model Grid:

The 21st century predicted by the HadCM3 climate model (one of those used by the IPCC) if a business-as-usual scenario is assumed for economic growth and greenhouse gas emissions. The average warming predicted by this model is 3.0°C.

Time evolution of globally averaged temperature change relative to the period 1961-1990. The top graph shows the results of greenhouse gas forcing, the bottom graph shows the results of greenhouse gas forcing plus aerosol forcing.

Time evolution of globally averaged precipitation change relative to the period 1961-1990. The top graph shows the results of greenhouse gas forcing, the bottom graph shows the results of greenhouse gas forcing plus aerosol forcing.

The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to assess the "risk of human-induced climate change". IPCC: first assessment report in 1990 second assessment report in 1995 third assessment report in 2001 fourth assessment report in 2007 Intergovernmental Panel on Climate Change (http://www.ipcc.ch)

IPCC reports should be the most authoritative reports on climate change, and are widely cited in almost any debate related to climate change. The reports have been influential in forming national and international responses to climate change. A small but vocal minority (less than 1.5%) of the scientists involved with the report have accused the IPCC of bias.

Evidence of some uncertainties: (1) The individual models often exhibit worse agreement with observations. (2) All models have shortcomings in their simulations of the present day climate of the stratosphere, which might limit the accuracy of predictions of future climate change. (3) There are problems in simulating natural seasonal variability. (4) Coupled climate models do not simulate with reasonable accuracy clouds and some related hydrological processes.

Confidence in the ability of models to project future climate has increased Simulated Annual Global Mean Surface Temperatures Volcanic and solar activity ghg and sulphate aerosols all (b) Able to explain most recent increases, but best fit given for (a)+(b) This doesn’t exclude the possibility other forcings have played a role too.

Global warming  Heating  Temperature  & Evaporation  water holding capacity   atmospheric moisture    greenhouse effect  & rain intensity  Floods & Droughts

Growing Cooperation Between Modelers and Field-Scientists “Your tools are terribly antiquated and imprecise” “You produce junk and waste a lot of money” Climate Modeler Field-Geologist Solution: interdisciplinary collaborations! Requirement: understanding each others ‘language’

7. Summary Climate change occurs through all time scales. Climate conditions at a given period are a result of complex interactions among components of the climate system driven by specific forcing factors. Climate modeling is a powerful approach to studying the cause-effect relationships. Observed data (proxy and instrumental) are critical for calibrating climate models. Understanding the causes and effects of global warming is one of the grandest challenges facing today’s scientists and the public.

Thank You!