climate change overview – pieces of the argument

Climate ChangeOverview – Pieces of the Argument

IPCC, 2007

Global Change and the Climate System

Change is as a result of:•greenhouse effect•natural processes•natural feedbacks to the greenhouse effect

wayne.edu, 2007

•atmosphere ~90 times denser than earth•97% CO2

•460oC despite thick clouds that limit sunincident at surface to 1/6 that of earth

little atmosphereno appreciable greenhouse

CO2 is the critical greenhouse gas

But not the only GHG of concern

IPCC 2007

IPCC 2007

The instrumental record

Global Averages? Bias?

NOAA, 2008

Are The Recent Changes Natural?

How do we determine the relative influence of natural and anthropogenic climate changes?

First Step: The proxy record.

Proxies are paleoclimatic indicators. Proxies are measured variables, used to infer temperatures.Many available, each with different strengths and utility.They allow us to know climate in its natural state.

What has climate looked like?

NOAA 2008

Variable.

http://cgc.rncan.gc.ca/baffin4d/proj/p02_e.phpVariable.

NOAA 2008

Variable.

But, natural variability is cyclic, especially at longer timescales. It is also shows predictable responsive to changes in forcing agents

• PROXY ( indirect methods)

– Tree-ring widths

– Ice Core data

– Sediment Varves

– Glacial Moraines

– And others

• Direct Methods

– Geothermal Data

What lines of proxy/paleoclimate evidence? Many.

Tree rings

• Ring widths record climatic information

Images: C. Laroque, MtA

Ice Cores

• Oxygen isotope analysis of gas bubbles – used to determine temperature at the time of precipitation

http://www.emporia.edu/earthsci/student/tinsley1/drilling.jpg

Corals

•Records the variability of the tropical and sub-tropical oceans and atmosphere, •prior to the instrumental period, •at annual or seasonal resolutions

Palaeoclimate reconstructions from corals generally rely on geochemical characteristics of the coral skeleton such as temporal variations in trace elements or stable isotopes.

Lake and ocean sediments

Physical and biological proxies-organisms that lived in the water whose remains are preserved-isotopes and other chemical signatures-texture-thickness of interannual layers called varves

Lake varves are great because they provide seasonal to interannual resolution over centuries to millennia. Three primary climate variables may influence lake varves: • summer temperature, serving as an index of the energy available to melt the seasonal snowpack, or snow and ice on glaciers• winter snowfall, which governs the volume of discharge capable of mobilising sediments when melting• rainfall.

From Timo J. Saarinen’s webpage

Documentary evidence

Some problems:• documents may be biased towards extreme events • inconsistent language • errors in dating.

Two areas where attempts have been somewhat successful:• Europe and China

Mountain glacier moraines

The position of moraines or till left behind by receding glaciers can provide information on the advances (and, less accurately, the retreats) of mountain glaciers.

An abandoned lateral moraine deposited when a glacier retreated

Boreholes – Unlike Proxies, a direct measure of temperature

• Like a tape recorder, the subsurface records the heat perturbations at the surface.

• Temperature increases with depth (it’s warmer the deeper you go!)

• Temperature increase through depth is linear and well known for standard conditions.

• Look for perturbations in this nice linear profile.

http://wayupnorth.files.wordpress.com/2006/06/borehole.jpg

Uses a mathematical/modeling technique called “Inversion”to calculate the ground temperature change over time that led to the measured T-depth profile.

Natural Variability

• Proxy record shows that climate has changed in the past, and will likely change in the future.

• Carbon dioxide concentrations also vary over time.

• What’s different? The current rate of change is unprecedented. Extremely abrupt.

• Attributing cause for the abrupt changes is done via another tool – the all-important Global Climate Models (GCMs).

EPA, 2009

As an aside - How much colder is a glaciation?

GCMs help assign blame for the recent observed variability

GCM Complexity

Through simulation, we can estimate the importance of our activities that are known to affect climate.

Other Pieces of the Climate Puzzle:

External climate factors that also vary over time:Earth’s orbitSolar radiationAerosols

Other mechanisms of climate changeOther greenhouse gasesHeat absorption capacity of atmosphere, oceansChanges in the distribution of heat, latent heatChanges in hydrological cycle intensityChanges in albedo

Feedbacks – Positive and negative

A complex picture! We’ll proceed one step at a time.