The document summarizes evidence of climate change from various scientific records and climate modeling. It discusses how ice core records show a link between atmospheric greenhouse gas concentrations and temperature over the past 450,000 years. It also notes that recent greenhouse gas levels far exceed those of the past. Climate models simulate past warming accurately when including human factors like increased greenhouse gases. The models predict continued accelerated warming this century if emissions are not reduced substantially. Observations also show impacts of warming already, such as sea ice and glacier melting, more extreme weather, and sea level rise.

1. Overview of Climate Change Science:
Fundamentals and Recent Developments
Prepared for the Climate Change and Adaptation Symposium
John Merrill,
URI GSO
November 18, 2011

2. Talk organization
I’ll present observational evidence of global warming, starting
with cycling between glacial and interglacial conditions over the
last half million years.
This will lead in to the role and impact of greenhouse gases,
their recent buildup and consequent rapid changes, ending with
information on how climate models are used to assess these
changes.
The figures are from the 2007 report of the Intergovernmental
Panel on Climate Change, a UN organization of scientists and
diplomats charged with bringing the best science to bear on the
underlying science and on policy issues.

3. Glacial-Interglacial Cycles - observational evidence
Data on atmospheric gases, collected from polar ice cores. Shaded
areas = Interglacial periods.

4. Gas concentrations
rise/fall over 1000s of
years.
Middle curves: CO2 - red,
CH4 (methane) - blue.
Oxygen isotope data =
ice volume and
temperature. T scale,
right.
(IPCC 2007) Brief warm periods with
high gas concentrations =
Interglacials.
Most of last 450 ky spent
in glacial conditions.

5. Ice core and instrumental gas data - last 2000 years
CO2 and CH4 concentrations over last 2 ky, including recent
instrumental data. Grey bands indicate range over prior 450 ky.

6. Note CO2 and CH4 now
far exceed paleo values.
These are greenhouse
gases.
Together with water
vapor, H2 O, they keep the
earth warm.
Emphasis on CO2 and
CH4 - they are altered by
humans, or
anthropogenically.
Increased greenhouse gas
concentrations and other
effects shift the global
(IPCC 2007) heat budget.

7. Induced heating from anthropogenic effects - Summary
Heating by greenhouse gases, and cooling by aerosols and land
use changes, over last 255 years.

8. Top two bars are heating
by changes in primary
anthropogenic
greenhouse gases.
Land use change example:
forest clearing.
Aerosols are particulates,
smoke, dust, haze.
Changes in solar heating
are smaller than
uncertainty.
Estimated heating minus
cooling shown in brown
bar.
(IPCC 2007)

9. Schematic of global thermal energy balance
Heating from sunlight in left half; cooling by emitted thermal
energy on right. Multiple sources of data required for each
quantity.

10. Quantitative summary of
heat balance of earth.
Thick bands on right
indicate atmosphere emits
almost as much as it
absorbs.
Greenhouse gases absorb
infared energy, heating
the atmosphere.
Increased amounts of
(IPCC 2007) these gases, increased
temperatures.

11. Evidence of warming in air temperature records
Global average land-surface air temperature over 1850 - 2003.
Bars are individual years; curves are smoothed estimates by
different groups. Continued warming in recent years.

12. Climate model simulations background
Simulations used to check our understanding of processes, and
to predict state of climate in times to come.
Numerical models simulate climate.
Most significant physical processes included.
Multiple models, using different approaches.
Simulations for prior years compared with observations.
Available computer power enables multidecadal runs.
Processes can be included/excluded to highlight effects.

13. Climate model simulations of temperature trends
Black, observed temperature; color, model estimates. Bottom, only
natural processes; top, including anthropogenic greenhouse gases.

14. Dozens of independent
simulations of a century
of climate.
In blue at bottom a
Hypothetical scenario:
steady GHG amounts.
In yellow/red at top
Realistic scenario of
increasing gases.
Vertical lines indicate
volcanic eruptions -
transient cooling events.
Increased gases must
cause the observed
warming.
(IPCC 2007)

15. Recently observed trends - impacts of warming
Arctic summer sea ice melt has reached record extent.
Coming exploitation of Arctic fossil fuel and fisheries resources
- troubling implications.
Rate of melting of Greenland and Arctic sea ice has increased
and is accelerating.
Warming of tundra - release of huge amounts of GHGs
trapped there.

16. Additional observed trends
The ocean’s heat content is increasing. Isaac’s talk.
Droughts more frequent and more intense.
Record high temperatures outnumber record lows by over
3:1.
Midlatitude storm tracks migrating towards the poles.
Climate zones are shifting toward the poles, by hundreds of
miles.
Floods becoming more frequent and more intense.
Ocean acidification impacting fish, corals and other biota.

17. Future scenarios simulated
Surface warming increment vs. time in various scenarios.
Numerals indicate number of model simulations aggregated.

18. The rate of temperature
rise is increasing.
That is, the warming is
accelerating.
5◦ C range = 9◦ F change.
Lleveling off only with
drastic changes, e.g. B1.
Temperature increase
expected even if all
emissions stopped now.
(IPCC 2007)

19. IPCC is a process as much as
a group. Their next Report is
being drafted now, and is to
be released in June, 2013.
Emissions of GHGs have
exceeded targets everywhere
and always, even with
curtailment steps.
Cautious scientists see
important impacts as “virtually
certain”.
(Wickford, 2011 - J. Denton)