How Do We Know the
Climate is Changing
Faster than Usual
➢Many scientists consider anthropogenic
global climate change to be the most
important environmental issue of our times.
➢1859 - John Tyndall measured the infrared
absorption of various gases and described the
➢1895 - Svante Arrhenius predicted that CO2
released by coal burning could cause global
MAUNA LOA OBSERVATORY
➢ Established in 1957 (part
of an Int’l Geophysical
➢ Intended to provide data
on air chemistry in remote,
➢ Where the first evidence of
CO2 due to human
activities came from
FIGURE 1: Measurements of atmospheric CO2 taken at the top of Mauna Loa, Hawaii show an increase of 1.5-
2.5 % each year in recent years. For CO2, monthly mean (red) and annual mean (black) CO2 are shown.
Temperature represents 5-year anomalies.
Scientific consensus is clear
➢ Climate scientists worldwide have collaborated in
collecting and sharing data and in programming
models to describe how the climate system works.
➢ The evidence shows unequivocally, as in the
Mauna Loa graph, that climate is changing and
the global average is warming because of
increased retention of energy in the lower
INTERGOVERNMENTAL PANEL ON CLIMATE
➢ Most comprehensive effort to
describe that state of climate
➢ A collaboration among governments,
with scientists and government
representatives from 130 countries
➢ Aim: to review scientific evidence on
the causes and likely effects of
human-caused climate change.
➢ 2007 - IPCC issued its Fourth Assessment Report
○ Four volumes of the report represent a
consensus by more than 90% of all the
scientists working on climate change.
○ Conclusion: 90% certainty that observed
climate change is caused by human activity
Changes in heat waves, sea level, and storms
➢ The Fourth Assessment Report presents a variety
of climate scenarios for predicted emissions of
➢ Scenarios differed in expected population growth,
economic growth, energy conservation and
efficiency and adoption of greenhouse gas
➢ About 2-4°C (about 3-8°F) - “best estimate” for
temperature rise now according to IPCC
➢ Observations since 2007 show that all the IPCC
scenarios were too conservative.
➢ Greenhouse gas emissions, temperatures, sea
level and energy use have accelerated faster than
projected by any of the IPCC projections.
➢ There is a serious concern that increased heat
stress and drought could cause increased deaths
as well as crop failure and new waves of refugees
from drought-stricken regions.
FIGURE 2: Emissions scenarios and
actual emissions observed after
scenarios were modelled.
“Climate change, national security, and energy
dependence are a related set of global challenges that will
lead to tensions even in stable regions of the world.”
- US Military Advisory Board, 2007
➢ The United States Military is concerned about global
➢ Some international aid agencies point to the civil war and
accompanying humanitarian crisis in the Darfur region of
○ These problems are rooted in drought and food
shortages caused by changing weather patterns that
have led to years of below normal rainfall and
➢ Climate scientists point out that shifting our energy strategy
from coal to wind, solar and greater efficiency could
produce millions of new jobs and save billions in health
care costs associated with coal burning.
➢ Since preindustrial times, atmospheric conditions of CO2,
methane (CH4) and nitrous oxide (N2O) have climbed by
over 31%, 151% and 17% respectively.
The main greenhouse gases are CO2, CH4, and
Carbon Dioxide (CO2) - most important because of its
abundance and lasts for decades for centuries in the
➢ Fossil fuel use - 80% of CO2 emissions
○ Other sources - cement production and burning of
forests and grasslands
○ 33 billion tons every year by average
Methane (CH4) - much less abundant than CO2 but absorbs
23 times as much as infrared energy per molecule and is
accumulating in the atmosphere about twice as fast as CO2
➢ Produced anywhere organic matter decays without
oxygen, especially under water
➢ Natural gas
➢ Released by ruminant animals,wetrice paddies, coal
mines, landfills, wetlands and pipeline leaks
➢ Reservoirs for hydroelectricity - important source of
CH4 because they capture submerged, decayed
Nitrous Oxide (N2O) - produced mainly by chem.reactions
between atmospheric N and O
➢ Other sources: burning of organic material and soil
Chlorofluorocarbons (CFCs) and other gases containing
Fluorine - store heat from infrared energy
FIGURE 3: Contributions to global warming (a) by different
gases and activities, (b) by different countries
Evidences of climate change is overwhelming
“As best as can be determined, the world is now warmer
than it has been in any point in the last two millennia and
if current trends continues, by the end of the century it
will likely be hotter than at any point in the last two million
- American Geophysical Union
➢ American Geophysical Union is one of the nation’s
largest and most respected scientific organizations.
Some of the evidences that led AGU to their conclusion:
1. Over the last century, the average global temperature has
climbed about 0.6°C (1°F).
2. Polar regions have warmed much faster than the rest of
3. Arctic sea ice is only half as thick now as it was 30 years
ago, and the area covered by summer sea ice has
decreased by about half in just three decades.
4. Ice shelves on the Antarctic Peninsula are breaking up and
5. Nearly all alpine glaciers are retreating rapidly.
6. So far, the oceans have been buffering the effects of our
greenhouse emissions both by absorbing CO2 directly and by
7. Sea level has risen worldwide approximately 15-20cm (6-8
in) in the past century.
8. Satellite images and surface measurements show that
growing seasons are now as much as three weeks longer in a
band across northern Eurasia and North America than they
were 30 years ago.
9. Droughts are becoming more frequent and widespread.
10. Biologists report that plants and animals are breeding
earlier or extending their range into new territory.
11. Coral reefs worldwide as “bleaching” as water
temperatures rise above 30°C (85°F).
12. Storms are becoming stronger and more damaging.
Controlling emissions is cheap compared to climate
➢ 2010 study by Pew Trust - evaluated estimates of the cost of
lost ecological services by 2100
○ Costs included factors such as:
■ Lost agricultural productivity from drought
■ Damage to infrastructure from flooding and storms
■ Lost biological productivity
■ Health costs from heat stress
■ Lost water supplies
Sir Nicholas Stern - estimated the immediate costs of climate
change would be at least 5% of the global GDP each year (British
➢ For many people, global climate change is a moral and
practical issue as well as a practical one.
➢ Religious leaders are joining with scientists and business
leader to campaign for measures to reduce greenhouse
➢ Scientific studies have long been unanimous about the
direction of climate trends but commentators on television,
newspapers and radio continue to fiercely dispute the
➢ Climate scientists offer the following responses to some of
the claims in the popular media:
1. Reducing climate change requires abandoning our current
way of life.
2. There is no alternative to current energy systems.
3. A comfortably lifestyle requires high CO2 output.
Why are there disputes over climate change?
4. Natural changes such as solar variation can explain
5. The climate has changed before, so this is nothing new.
6. Temperature changes are leveling off.
7. We had cool temperatures and snowstorms last year, not
heat and drought.
8. Climate scientists don’t know everything, and they have
made errors and misstatements.