Here are key highlights from the Summary
for Policymakers that the Inter-governmental
Panel on Climate Change (IPCC) released on 27 September, with new
findings on the physical basis of climate changes, as it wraps up
its Fifth Assessment (Climate
Confidence in a human influence on
climate changes: “It is extremely likely that
human influence has been the dominant cause of observed warming
since the mid-20th century.” An outcome is considered extremely
likely if there is a better than 95% chance that it is truly happening.
A “budget” of fossil-fuel carbon for all
time is needed to stabilize climate: For perhaps the
first time, the IPCC prescribed a limit to the total carbon in fossil
fuels that can ever be extracted and burned, while keeping the warming
of the Earth (since 1870) to 2°C or less. That limit is 1 trillion
tons of carbon in all fossil fuels, if CO2 if the only
greenhouse gas considered. The IPCC estimates (with a certainty
of 66%) that global warming will not exceed 2°, if that budget
Why two degrees? The United
Nations Framework Convention on Climate Change set a goal of limiting
emissions of greenhouse gases at a level that “prevents dangerous
interference in the climate system.” The science academies
of several nations have stated that a 2°C limit on total global
warming does avoid dangerous interference.
A sobering reality check
is that already 530 billion tons of carbon in fossil fuels—over
50% of the “budget”—have been burned and released
as CO2 by 2011.
Amount of warming: From
1880 to 2012, the surface of the Earth warmed on average by +0.85°C
(1.5°F); since 1901, almost the entire globe experienced surface
Recent hiatus in warming: Trends based
on short periods (such as the last 15 years) do not reflect longer
trends (such as over a century), because climate naturally varies
year-to-year and over short periods of time.
Extreme rainfall: Precipitation has
increased over land in the middle latitudes of the Northern Hemisphere
-- there is high confidence in an increase after 1950, and only
medium confidence before 1950. Heavy precipitation events have become
more frequent and more intense over Europe and North America.
Ocean warming: The Ocean has stored
more than 90% of the energy retained on Earth due to global warming
from 1971 to 2010. It is certain that the ocean warmed in the last
40 years, when measurements were good, and likely warmed in the
100 years before 1970.
Loss of polar ice: The Greenland ice
sheet has lost ice five times faster in the last ten years
than it lost in the previous ten years.
Sea level: Sea level began to rise at
a faster rate over 110 years ago, but the current rate of rise is
about twice the rate observed since 1901.
CO2 levels: Concentrations
of CO2 are measured in bubbles found in ice cores taken
from the great ice sheets of Antarctica. Current concentrations
of CO2 and methane in the atmosphere exceed the highest
levels measured in ice core bubbles from the last 800,000 years.
Translation: the level of CO2 in the atmosphere has never
been as high (in the last 8000 centuries) as it is now.
The Medieval warm period: The IPCC now
states that the last thirty years (1983–2012) “was likely
the warmest 30-year period in the last 1400 years” or since
600 A.D., in the Dark Ages. This implies that our current climate
is now warmer than the Medieval Warm period, which some scientists
thought was as warm as the present.
State of the Climate:
Three Reports to Note
quite different assessments of the state of the current climate
and its changes appear this year:
every six years, an international team of scientists deliberates
and writes a thorough review of climate change to date, with prognoses
for future climate for the next 100 years. This month, the Intergovernmental
Panel on Climate Change (IPCC) releases its fifth such
assessment report since 1990; and it announces a new summary
for policymakers on Friday, September 27 (link,
On Monday, September 30, the IPCC releases online the full draft
report on the physical basis for climate change, including a technical
summary, 14 chapters and 3 annexes. We report some key findings
here at left. Some 209 lead authors and 50 review editors from 39
countries contributed to its preparation.
of the Climate in 2012” (footnote
2) is the 23rd such report produced by the US National Climatic
Data Center and published annually by the American Meteorological
Society (AMS) since 1990. It no longer focuses traditionally on
the climate of the atmosphere, but reports changes in the entire
Earth "system" including the Ocean (currents, salinity,
heat content, circulation, sea level, and more), the realm of ice
on land and sea, the land cover and vegetation, the hydrological
cycle including rivers and soil moisture, and the carbon cycle.
Some 415 authors and editors
from dozens of nations contributed to this year's State of the Climate.
As usual, the largest section is devoted to regional climates on
seven continents or continental regions, including changes from
World Meteorological Organization (WMO, footnote
3) also puts out an annual report on climate for the previous
year. With only 33 pages, their most recent “Status
of the Global Climate in 2012” is attractively
illustrated and easily readable in one sitting. In contrast to the
above publications, the editors clearly wrote it for general readers,
not for scientific or specialist audiences.
1. The IPCC, based in Geneva, Switzerland,
resides on the internet at http://www.ipcc.ch/
of the Climate in 2012,” by J. Blunden and D.S. Arndt,
editors, 2013. Special supplement to the Bulletin of the American
Meteorological Society, vol. 94, number 8,
pages S1–S238, 256 pp.
statement on the Status of the Global Climate in 2012”
–World Meteorological Organization, no. 1108, Geneva, 2013,