Scientists are 90% sure humans are responsible for global warming

I read several parts of the 3rd IPCC asssessment report when I was in the process of compiling my Ph.D thesis. Several colleagues and professors had been contributors, and I was fascinated how a topic that had such high agreement within the scientists was still deeply conetentious in the public press and media. and that too about the science. It was unbelievable that Texas (not only) politicians were questioning the sceintific facts even without looking at the data.

Now the new IPCC report has been published, and once again, with even clearer technical data, and pursuasive scientific arguments, one of the largest global teams of scientists working together have announced that (a) global warming is happening – and is getting worse, and (b) there is >90% chance that human beings are responsible for it. Our Co2 emissions, coupled with emissions of methane, DMS, sulfates, soot etc are all contributing to it. A wonderful summary of the results has been done by Green Car Congress’ Mike Milliken. See here. The official IPCC summary document is here.

The only big question left for me in this debate is: what are we doing about it? Kyoto protocol is dead and the regulatory networks around the world are moving at a dastardly slow pace in regulating the fuel economies and CO2 emissions from vehicles and industries. US may, in the next 5 years move to a cap-and-trade system for CO2 emissions but even that will only show effects over a very long time. I think our modern day governments and institutions are, frankly, failing us in this regard. So I vote to make an average citizen in chanrge and let them play the critical role in forcing a change in our behavior.Here’s an idea: Can an average consumer participate in the global carbon credit trading system and benefit from it while moving to a lower carbon lifestyle? No, not the Terrapass type feel-good buy-some-carbon-credit-and-still-do-what-you-do stuff, but actually finding a consumer benefit in reducing waste and emissions? Can we insititute tax credits for consumers if they have lower annual carbon foot print? Will they get their sales tax (or equivalent in other countries) back if they purchase a lower carbon product when a cheaper higher carbon emittin product was available?

Sam’s Club and Tesco are starting to put the Carbon content on their products (as Terrapass reported). Can we build a reliable and verfiable system so individuals could trade their carbon credits and at the same time get financial benefits for having a reduced carbon foot print? What about linking it to college loans or PEL grants programs? I am just thinking aloud –> I am sure there are many ways to cut this pie and some would make for great startup ideas!!!

Here’s a summary of the IPCC Working Group I report. Thanks to the Union of Concerned Scientists in the USA for this. All credits to them:

********EXECUTIVE SUMMARY ********

This morning, the Intergovernmental Panel on Climate Change (IPCC) released
its first installment on the state of climate change science. This Summary
for Policy Makers (SPM) synthesizes the current understanding of the human
influence on climate change, observed evidence of warming, and projects
future climate using the most comprehensive set of well-established global
climate models. Today’s findings conclude that it is “unequivocal” that the
Earth’s climate is warming; that current atmospheric concentration of CO2
far exceeds the natural range of the last 650,000 years; and that it is
“very likely” (>90%) that human heat-trapping emissions are the cause.

******* THE ISSUE

After assessing six years of climate research from the depths of the oceans
to the outer reaches of Earth’s atmosphere, scientists from around the world
have reported on the major advances in understanding about climate change.
The IPCC’s Fourth Assessment (AR4) includes input from over 1200 authors and
2500 scientific expert reviewers from 130 countries. The full AR4 will be
comprised of three sections, or working groups, that deal with the
scientific basis of global warming (Working Group I), its consequences
(Working Group II), and options for slowing the trend (Working Group III).
The IPCC will release summaries of the three working group documents over
the course of 2007, culminating in the publication of the final “synthesis
report” at the end of the year.

Key findings from the Working Group I Summary for Policy Makers (SPM) are
below. These are also available on our website, along with a backgrounder on
the IPCC Process.

*** Highlights from the First Section of the IPCC Fourth Assessment Report

Note: Whenever possible exact language from the IPPC is used throughout. To
enhance clarity, slight modifications were made that maintain the intended
meaning of the report.

After assessing six years of climate research from the depths of the oceans
to the outer reaches of Earth’s atmosphere, scientists from around the world
have reported on the major advances in understanding about climate change.

The new IPCC Working Group I Summary for Policymakers synthesizes the
current understanding of global warming and projects future change using the
most comprehensive set of well-established global climate models. The
report is the first of three major studies that comprise the full IPCC
Fourth Assessment, which includes input from more than 1,200 authors and
2,500 scientific expert reviewers from more than 130 countries. Subsequent
reports will evaluate global warming consequences and options for reducing
future warming.

IPCC Range of Likelihood
When the IPCC describes the likelihood of an event, the term used reflects a
percent range of likelihood, as defined below:

< 5% = Extremely Unlikely
< 10% = Very Unlikely
< 33% = Unlikely
< 50% = Less likely than not
> 50% = More likely than not
> 66% = Likely
> 90% = Very Likely
> 95% = Extremely Likely

Updated Assessment of the Human Impact on Climate
Evidence that human activities are the major driver of recent climate change
is even stronger than in prior assessments. (1) According to the summary,
there is a greater than 90 percent likelihood that increased concentrations
of man-made heat-trapping gases caused most of the observed increase in
global average temperatures since 1950.

Advanced Understanding of Recent Climate Change

The report also concludes that it is “unequivocal” that Earth’s climate is
warming “as is now evident from observations of increases in global average
air and ocean temperatures, widespread melting of snow and ice, and rising
global mean sea level.”

The report confirms that the current atmospheric concentration of carbon
dioxide, a critical heat-trapping gas, “exceeds by far the natural range
over the last 650,000 years.” Since the dawn of the industrial era, carbon
dioxide and other key heat-trapping gases have increased at a rate that is
“very likely to have been unprecedented in more than 10,000 years.”

Other IPCC Observations of Current Climate Change:


* Eleven of the last twelve years rank among the twelve hottest years on

* Over the last fifty years, cold days, cold nights, and frost have become
less frequent, while hot days, hot nights, and heat waves have become more

Extreme Weather Trends (storms, precipitation, drought)
* Observations show an increase of intense tropical cyclone activity
(hurricanes and typhoons) in the North Atlantic since about 1970, correlated
with increases of tropical sea surface temperatures. There is some evidence
for increased intensity of tropical cyclone activity in some other regions.
The report has found no clear trend in the annual number of tropical

* As expected with warming and the resulting observed increases in water
vapor, the frequency of heavy precipitation events has increased over most
land areas. Between 1900 and 2005, long-term trends show significantly
increased precipitation in eastern parts of North and South America,
northern Europe and northern and central Asia.

* Between 1900 and 2005, drying has been observed in the Sahel (the boundary
zone in Africa between the Sahara desert and the more fertile region to the
south), the Mediterranean, southern Africa, and parts of southern Asia.

* More intense and longer droughts have been observed over wider areas since
the 1970s, particularly in the tropics and subtropics.

* Droughts have been linked to changes in sea surface temperatures and wind
patterns and decreased snowpack and snow cover.

Melting of Frozen Regions

* The maximum area covered by seasonally frozen ground has decreased by
about 7 percent in the Northern Hemisphere since 1900, with a decrease in
spring of up to 15 percent.

* Mountain glaciers and snow cover have declined on average in both

* Satellite data since 1978 show that arctic sea ice extent during the
summer has shrunk by over 20 percent.

Sea Level Rise
* The world’s oceans have been absorbing more than 80 percent of the heat
added to the climate, causing ocean water to expand and contributing to sea
level rise.

* Melting glaciers and ice caps, and losses from the Greenland and Antarctic
ice sheets have contributed to recent sea level rise.

Refined Projections of Future Climate Change
Projected climate change for the end of the 21st century depends on the
level of future emissions. The IPCC used six defined emission scenarios,
plugging each scenario into sophisticated climate simulation computer

Even if we act today to reduce our emissions from cars, power plants, and
other sources, past emissions will commit us to more warming since they stay
in the atmosphere for decades. The report concludes that if we take no
action to reduce emissions, there will be twice as much warming over the
next two decades than if we had stabilized heat-trapping gases at 2000

Other IPCC Projections: (2)

* The full range of projected temperature increase is 1.1 to 6.4 °C (2 to
11.5 °F)

* The best estimate range, which reflects the center point of the lowest and
highest emissions scenarios, is 1.8 to 4.0 °C (3.1 to 7.2 °F).

* Warming is expected to be greatest over land and at most high northern
latitudes, and least over the Southern Ocean and parts of the North Atlantic

Extreme Weather Trends (storms, precipitation, drought)
* It is likely that future tropical cyclones (typhoons and hurricanes) will
become more intense, with higher peak wind speeds and more heavy
precipitation associated with warmer tropical seas.

* Increases in high latitude precipitation are very likely, while decreases
are likely in most sub-tropical land regions (e.g. the Middle East).

* There is a greater than 90 percent likelihood that extreme heat, longer
heat waves, and heavy precipitation events will continue to become more

Melting of Frozen Regions
* Sea ice is projected to shrink in both the Arctic and Antarctic under all
simulations. Some models show that by the latter part of the 21st century
Arctic late summer sea ice will disappear almost entirely.

Changes in the Ocean

* Models suggest that if global average warming were to exceed 1.9 to 4.6
degrees C (3.4 to 8.3 degrees F) compared to pre-industrial temperatures,
the Greenland ice sheet would lose mass faster than it gains, producing a
net contribution to sea level rise. If sustained, the loss of ice would
eventually lead to complete elimination of the Greenland ice sheet and
contribute an additional 23 feet to sea level rise.

* It is very likely that the so-called “conveyer belt ocean circulation” in
the North Atlantic region will slow down during the 21st century. The
average reduction estimated by the models is 25 % by 2100. However, despite
such changes, Atlantic region temperatures are projected to rise due to more
significant warming from increases in heat-trapping emissions.

* Increasing atmospheric carbon dioxide concentrations will lead to
increasing acidification of the ocean.
Clarification on the Report’s Sea Level Rise Projections
It is important to understand what is and is not included in the report’s
sea level rise projections. There are several factors that contribute to
average sea level (all of which are caused by warming) and these are
assessed separately in the IPCC report. These include:

* Ocean expansion resulting from increased ocean temperature

* Meltwater runoff from mountain glaciers and small ice caps

* Meltwater runoff and calving ice blocks from the two large ice sheets
(Greenland and Antarctica).

The models used by the IPCC project that by the end of this century, global
average sea level will rise between 0.18 and 0.59 meters (7 to 23 inches)
above 1980-1999 average sea level.

The range for projected sea level rise has narrowed since the prior IPCC
assessment, which projected a range of 0.09 to 0.88 meters (3.5 to 34.6
inches). This narrower range reflects an improved understanding of some
processes that influence sea level (e.g. ocean heat content). However, the
report acknowledges that other unaccounted for processes make the high end
projection conservative.

Due to current uncertainties, the IPCC notes that the following factors are
not fully reflected in the current generation of IPCC models:

* Evidence suggests that warming tends to reduce land and ocean uptake of
atmospheric carbon dioxide, increasing the portion of man-made emissions
that remain in the atmosphere. This would result in further warming and
cause additional sea-level rise.

* Observations record that meltwater can run down fissures and lubricate the
bottom of ice sheets, resulting in faster ice flow and the calving of large
ice masses into the ocean. This process directly contributes to sea level

The sea level projections include observed contributions from the Greenland
and Antarctic ice sheets between 1992 and 2003, but exclude future changes
in ice sheet behavior because of limited understanding of how to quantify
potential changes from this source. For example, the IPCC states, “if this
contribution were to grow with global average temperature change,” the worst
case scenario “would increase by 0.1 to 0.2” meters (3.9 to 7.9 inches). In
other words, the high range for sea level rise in this example could be 0.79
meters (31 inches).

(1) The Third Assessment Report (TAR 2001) concluded that “most of the
observed warming over the last 50 years is likely to have been due to the
increase in greenhouse gas concentration.”

(2) Future climate predictions rely heavily on the commonly referred to
“climate sensitivity” test, which is based on climate model analyses
together with observations and is defined as the global average surface
warming following a doubling of carbon dioxide concentrations (around 550
ppm). Under this test it is likely that temperatures will increase between
2.0 to 4.5 °C (3.6 to 8.1°F) above pre-industrial levels with a best
estimate of about 3.0 °C (5.4 °F).

(3) Projected reduction in average global surface ocean pH are between 0.14
and 0.35 units over the 21st century adding to the present decrease of 0.1
units since pre-industrial times.


4 Responses to Scientists are 90% sure humans are responsible for global warming

  1. Manas says:

    I am sorry, but what is carbon credit?

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