Climate Change

1. Climate State: is described in terms of an average value, a measure of variation about the mean, the extreme values, and the shape of frequency distribution (30 yrs).

2. Change in climate can occur in several different ways

(1) Shift in the mean; (2) graduate trend in the mean; (3) variability (periodic; quasi-periodic; non-periodic) (handout figure 11.1)

3. Observed changes can be real or artifact of changes in instrumentation, observational practices, station location, or the surroundings of the instrumental site, or due to errors in the transcribed data.

4. Causes of changes: difficult to ascribe because of the complexity of the climate system. Natural variability operates over a wide range of time scales and superimposed on effects of human activities.

Climate system (handout question 1.1)

A complex, interactive system consisting of the atmosphere, land surface, snow and ice, oceans and other bodies of water, and living things.

Climate changes in respond to changes in external factors and internal dynamics.

Three fundamental ways to change climate:

(1) Incoming solar radiation(2) reflectivity of the earth

(albedo)(3) longwave radiation from the

earth towards the space

Energy balance of the earth system (Figure 1)

(1) About 30% solar radiation is reflected back to space

(2) about 49% solar radiation is absorbed by the earth’s surface

(3) greenhouse gases absorb most of the longwave radiation from the earth and keep the earth warm.

Greenhouse effect

Greenhouse gases: CO2, H2O,CH4 ,N2O,O3,CFCs

Atmospheric effect = blanket effect: greenhouse gases absorb longwave radiation from the earth and re-radiate back to the earth, keep the earth warm (Fig 1.3)

Anthropogenic related climate warming: human activities increases greenhouse gases and increases earth’s surface air temperature

Radiative forcing: is a measure of how the energy balance of earth-atmosphere system is influenced when factors that affect climate are altered. Positive forcing lead to increase energy and warming, negative is decreasing energy and cooling.

Climate Forcings

External forcings (outside of the earth’s system)

1. Solar variability: 11-year solar cycle (sunspots), 22-year magnetic field cycle (solar flare).

2. Tectonic processes: changes in continental positions, sizes, and in the configuration of ocean basins, location and size of mountain ranges and plateaus modify the atmospheric and ocean circulation at geological time scales.

3. Astronomicalperiodicities: (1) eccentricity of the

orbit changes at a period of 95,000-410,000 years;

(2) the tilt of the earth’s axis has a period of 41,000 years;

(3) a wobble in earth’s axis of rotation causes changes in the timing of perihelion at time scale of about 21,000 years (handout figure 11.3)

4. Volcanic eruption: major explosive eruptions inject dusts and sulfur dioxide aerosols into the stratosphere, cause a hemispheric/global cooling of 0.5-1.0C in the year following the events

5. Atmospheric composition: changes in CO2 and CH4 and global temperature are coincident during both glacial and interglacial transitions.

Internal forcing

Involves in changes in atmospheric composition, cloud cover, aerosols and surface albedo that affects climate through a set of feedback mechanisms of positive (self-enhancing) or negative (self-regulating or damping) processes.

Example:Increasing temperature

Increases in water vaporIncreases in plant respirationDecreases in CO2 dissolved in the oceansIncreases CH4 emissions from wetlands

Increases in greenhouse gases

Global-average radiative forcing estimates Global-average radiative forcing estimates and ranges and ranges (handout Question 2.1, Fig2)(handout Question 2.1, Fig2)

Gradual cooling about 40-50 million years ago is theorized due to the formation of the Himalayan Mountain system during the Paleocene and Eocene epochs caused an increase in chemical reactions between newly exposed tock of the mountain system and the atmosphere that reduced CO2 level (Uplift Weathering Hypothesis)We currently live in the latest interglacial, known as the Holocene Epoch, began about 10,000 years ago.

Climate records

1. Paleo-records (10,000-23,000 years): proxy data from pollens preserved in lake sediments and peat bogs for vegetation info; former lake shorelines for moisture info; annual snow/ice layer in ice cores for seasonal change information; micro-particles and chemical compounds in the ice for volcanic events; tree ring for moisture and summer temperature(1500); historical documents record of crop harvests or extreme weather events; isotopes in sediments and ice cores; etc.

2. Instrumental records (since 1861)

Climate data derived from geologic indicators and other sources rather than instrumental records. (Fossilized plankton, coral from sediments on seafloors, chemical telltales from ice sheet, glaciers)Ice drilling:Ice core: air trapped in the glacial can derive CO2 level to approx temperature

Ocean floor drilling:Fossil Plankton (from phylum Foraminifera)provide chemical clues to the climate when they were formed

Global mean temperatures are rising faster with time

100 0.0740.018

50 0.1280.026

Warmest 12 years:1998,2005,2003,2002,2004,200

6, 2001,1997,1995,1999,1990,200

0

Period Rate

Years /decade

Warming in the Arctic is double that for the globe from 19th to 21st century and from late 1960s to present.

Warmth 1925 to 1950 in Arctic was not as widespread as recent global warmth.

Note different scales

Arctic vs Global annual temperature anomalies (°C)

CO2, CH4 and N2O Concentrations

- far exceed pre-industrial values- increased markedly since 1750

due to human activities

Relatively little variation beforethe industrial era

Human and Natural Drivers of Climate Change

Projections of Future Changes in Climate

Best estimate for low scenario (B1) is 1.8°C (likely range is 1.1°C to 2.9°C), and for high scenario (A1FI) is 4.0°C (likely range is 2.4°C to 6.4°C).

Broadly consistent with span quoted for SRES in TAR, but not directly comparable

Attribution

Asks whether observed changes are consistent with expected responses to forcings (red)inconsistent with alternative explanations

TS-23All forcings-blackNatural forcings only-blue

Data analysis

• Load data in excel sheet (or cut and paste) and reformat• Correlation analysis• Trend identification (simple linear regression with Time

as independent variable and the variable examining as dependent variable, Temp=a+b*Time). To simplify the project for this class, we only need to calculation correlation between the variable and the Time.

Correlation analysis

• To determine the strength of relationship between 2 variables (based on how they change with time or space).

• -1.0 to 1.0

• Use Pearson’s correlation analysis

• Significant test: the significant value used most common is 95% (or 0.05) confidence level. The value of correlation coefficient associated with this significance level is depend on the sample size.

MicrobiologyBytes: Maths & Computers for Biologists: Correlation coefficient

Updated: October 15, 2004 Search

Critical Values of the Correlation Coefficient If your degree of freedom is not on this table, use the value for next lower degree of freedom:

Level of Significance (p) for a Two-Tailed Test

df (n-2): 0.10 0.05 0.02 0.01

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 35 40 45 50 60 70 80 90 100

0.988 0.900 0.805 0.729 0.669 0.622  0.582 0.549 0.521 0.497 0.476 0.458 0.441 0.426 0.412 0.400 0.389 0.378 0.369 0.360 0.352 0.344 0.337 0.330 0.323 0.317 0.311 0.306 0.301 0.296 0.275 0.257 0.243 0.231 0.211 0.195 0.183 0.173 0.164

0.997 0.950 0.878 0.811 0.754 0.707 0.666 0.632 0.602 0.576 0.553 0.532 0.514 0.497 0.482 0.468 0.456 0.444 0.433 0.423 0.413 0.404 0.396 0.388 0.381 0.374 0.367 0.361 0.355 0.349 0.325 0.304 0.288 0.273 0.250 0.232 0.217 0.205 0.195

0.9995 0.980 0.934 0.882 0.833 0.789 0.750 0.716 0.685 0.658 0.634 0.612 0.592 0.574 0.558 0.542 0.528 0.516 0.503 0.492 0.482 0.472 0.462 0.453 0.445 0.437 0.430 0.423 0.416 0.409 0.381 0.358 0.338 0.322 0.295 0.274 0.256 0.242 0.230

0.9999 0.990 0.959 0.917 0.874 0.834 0.798 0.765 0.735 0.708 0.684 0.661 0.641 0.623 0.606 0.590 0.575 0.561 0.549 0.537 0.526 0.515 0.505 0.496 0.487 0.479 0.471 0.463 0.456 0.449 0.418 0.393 0.372 0.354 0.325 0.303 0.283 0.267 0.254