Climate Change

Temperature – A Critical Environmental Variable Life can be described very simply as a

series of well-regulated biochemical reactions.

Most of the reactions are controlled by specialized proteins called enzymes.

Temperature is critical to biochemical reactions, because it determines the effectiveness of the enzymes controlling the reactions.

Temperature – A Critical Environmental Variable When temperature

is either too low or too high, enzyme activity is reduced.  Goldilocks

principle

Temperature – A Critical Environmental Variable Temperature can similarly

affect the performance of entire organisms.

A Goldilocks-like relationship between temperature and performance is often seen in ectotherms, organisms whose body temperature depends on the surrounding environment.

Temperature – A Critical Environmental Variable Temperature also

affects groups of organisms.

Population growth rates and thus population dynamics may also follow the Goldilocks Principle, with growth rates maximized at some optimal temperature.

Temperature – A Critical Environmental Variable At global scales,

species richness—the number of species in a given area—tends to be highest in the tropics and lowest near the poles.

Much of this variation can be explained by temperature.

Detecting Climate Change

Detecting Climate Change The climate on Earth is continually

changing. Several ice ages have come and gone. The lower temperatures and altered rain

patterns during the ice ages produced a world very different than today's. Northern forests were replaced by large

expanses of tundra as cool, dry air rolling off the ice sheets pushed tree habitats southward.

Detecting Climate Change Climate continues to change today as it

has always done in the past. We can use statistics to monitor

changes. We need to know whether the changes

are due to the same factors as in the past. Attribution

Climate vs Weather Weather describes short-term behavior

of the atmosphere. Time scale: minutes to months

Climate describes a region's average weather conditions over a long time period, and how much those conditions vary. Time scale: 30 years +

Detecting Trends To investigate climate change, we need

to detect trends in the climate.  Detecting such trends in climate, even

when they are known to exist, is difficult because of weather.

Variability (i.e "noise" in the data) can make it difficult to detect trends ("signal").

Detecting Trends Sometimes the trends are easy to see.

p < 0.0001

Detecting Trends Sometimes they are a bit harder to detect.

p = 0.0025

Detecting Trends It is easier to detect a trend with a

larger signal. When the signal was small

(0.005 °C/year), the trend was difficult to detect even though we know it was there, while larger signals were easier to detect with simple regression analysis.

Detecting Signals The amount of noise also affects our

ability to see the trends.

5 Components of Earth’s Climate System Atmosphere - air Hydrosphere - water Cryosphere – frozen water Lithosphere – rocks & soil Biosphere – living organisms

Trends in the 5 components If Earth's climate is changing then we should find

predictable, directional changes in all five components of the climate system.

If the data show that each component is changing in a way that is consistent with a warming (or cooling) climate, we have more faith in concluding that Earth's climate as a whole is changing.

Conversely, if each component is changing independently and in different directions, we will conclude that the Earth is not, on average, warming or cooling.

Measuring Temperature Over Time - Atmosphere This animation suggests that Earth has

warmed and that this warming is not regional but has occurred across much of the globe.

Measuring Temperature Over Time - Atmosphere The IPCC climatologists found that

Earth's mean annual temperature increased about 0.74 °C over the past 100 years (1906-2005).

Measuring Temperature Over Time - Biosphere Because the growth and population

dynamics of many organisms—including trees and other plants, corals, plankton, and insects—vary predictably in response to changing climates, in a sense, these organisms record ancient climates.

Measuring Temperature Over Time - Biosphere As trees grow, new wood is laid

down just under the bark in annual layers that can be seen as tree growth rings.

In good years, the tree grows faster, giving a wider ring for that year.

By measuring the variation in tree ring width, it's possible to reconstruct how temperature and precipitation have varied over the life of a tree.

Measuring Temperature Over Time - Cryosphere If the Earth is warming, we would expect

that the Earth's snow and ice should melt faster each year.

Measuring Temperature Over Time - Cryosphere The dramatic reduction in the Arctic's

annual sea ice minimum has been accompanied by a decline in perennial sea ice, the thick, year-round ice cover.

Many mountain glaciers retreated over the past 50 years or so.

Measuring Temperature Over Time - Cryosphere

1941 2004

Measuring Temperature Over Time - Hydrosphere Climatologists have hypothesized that

the amount, intensity, frequency and type of precipitation will change. 

At much larger scales, warmer temperatures may be affecting the behavior of critical climate phenomena like El Niño and La Niña, which can affect precipitation patterns across much of the globe.

Measuring Temperature Over Time - Hydrosphere Warmer temperatures

can simultaneously produce both more intense storms in places where the air is saturated and more extreme droughts where it is not, even if the total amount of precipitation is not changing.

Sea Level Rise Changes in

precipitation, evaporation, storage and runoff—in particular from melting ice sheets and glaciers—can change the amount of water in the ocean.

Earth’s Climate and Climate Models

Greenhouse Gases Atmosphere is important in determining

a planet’s temperature. Earth is now warm enough to have

large, unfrozen oceans because its atmosphere acts like a blanket, trapping heat and thereby raising surface temperatures.

This is the greenhouse effect, which makes life possible here on Earth.

Greenhouse Gases The key to the greenhouse effect lies in

the difference in wavelength between incoming and outgoing radiation. 

Greenhouse Gases Nitrogen and oxygen (N2 and O2), gases

constituting the bulk of Earth's atmosphere, are transparent to both long and short wavelengths.

But greenhouse gases like CO2, CH4, and H2O, absorb the longwave radiation that is radiated from Earth's surface.

The energy these gases absorb is eventually re-radiated in all directions, including back toward Earth, where it raises the average surface temperature from -19 °C to 15 °C.

Modeling Climate Change Models reflect our current

understanding of climate and allow scientists to test hypotheses about factors affecting it.

Modeling Climate Change A planet's equilibrium surface temperature can be

predicted from a simple climate model that accounts for: Solar output, the energy warming a planet, which

varies over time. Distance from the Sun, which determines the

amount of solar radiation intercepted by a planet. Albedo, describing what proportion of incident solar

radiation is reflected. Greenhouse gases produce the "greenhouse

effect," further warming the surface of planets with atmospheres containing them.

Modeling Climate Change More complex models describe non-

equilibrium systems and incorporate climate feedbacks like the ice-albedo feedback loop.

Global circulation models (GCMs) are even more complex, incorporating a layered atmosphere, 3-dimensional spinning sphere structure, complex topography, and layered oceans.

Modeling Climate Change Current GCMs can accurately reproduce

recent large-scale patterns in average temperature. They are increasingly able to simulate smaller-scale phenomena like El Niño.

Humans and Climate Change

Attribution of Recent Climate Change Natural climate forcings typically

include aerosols from volcanic eruptions, plus changes in solar irradiation resulting from variation in the Earth's orbit or in solar output.

Anthropogenic climate forcings result from human actions and include greenhouse gas and man-made aerosol emissions, changes in land use, and exhaust from jet airplanes.

Attribution of Recent Climate Change Although solar

output varies, changes are too small to account for observed increases in average surface temperature on Earth.

Attribution of Recent Climate Change Since the 1850s,

concentrations of CO2 and other greenhouse gases have increased markedly, primary from fossil fuel combustion. Evidence comes from measurements made directly (e.g., Keeling's) and indirectly (e.g., from air bubbles trapped in ice).

Attribution of Recent Climate Change Models suggest that observed warming

is probably a direct result of increases in greenhouse gases.

Attribution of Recent Climate Change Climate models are used to forecast

how Earth's climate will respond to different IPCC emission scenarios.

These models predict an increase of between 1.8 °C and 4.0 °C by 2100.

Future Climate Change The IPCC estimated the

likely climate response to Increasing Affluence (A1B), Regionality (A2), and Green Growth (B1) scenarios with 20 GCMs. They also added a baseline scenario that assumed, optimistically, that CO2 concentrations were held constant after 2000.

How Will Climate Change Affect Us? Likely, high latitudes will warm more

than mid-latitudes, land surfaces will warm more than oceans, and precipitation patterns will change.

How Will Climate Change Affect Us? Heat waves, droughts

and severe storms are likely to increase.

Ecosystems will be affected by ocean acidification and altered patterns of primary production and respiration.

How Will Climate Change Affect Us? Further changes may occur abruptly and

unexpectedly. Human populations are likely to be strongly and negatively affected.

Biological Consequences of Climate Change

How Can Species Avoid Extinction Due to Climate Change? Species may move. Species may acclimate. Species may evolve.

Effect on Timing Climate change may

affect phenology, the timing of life-history events.

Springtime events like flowering are expected to occur earlier while autumnal events like migration or hibernation are expected to occur later.

Increased temperature leads to faster development times in butterflies.

Mismatches in Timing Altered phenologies

may produce mismatches between predators and prey or flowers and pollinators, reducing the population growth rate of one or both species.

Fitness Varies with Temperature An individual's

fitness can vary with temperature, often summarized using a temperature performance curve.

Range Shifts Species

distributions are expected to shift poleward or uphill in response to climate change.

Changes to Community Dynamics Because species

distributions change independently, climate change may alter both community composition and community dynamics.

Pine bark beetles survive better in milder winters – spread disease in coniferous forests.

Acclimation to New Conditions Another possible response is

to acclimate to the new climate. An individual may be able to adjust so

that its temperature performance curve changes and is better suited to the new temperature.

Adaptation to New Conditions Species may adapt

to climate change through evolution by natural selection, which can alter the species' temperature performance curve.

Time elapsed: 100 years

Adaptation to New Conditions A species' ability to evolve adaptations

to climate change depends on the rate of climate change and the species' genetic variation and generation time.

Adaptation to New Conditions Caribou of Greenland mature

slowly, can live 10 years or longer, and do not begin to reproduce until they are 3-4 years old.

This difference in generation time means that, for any given rate of warming, caribou and other long-lived species experience more warming per generation than do insects and other short-lived organisms.