The document discusses recent developments in climate science since the IPCC AR4, highlighting significant declines in Arctic sea ice extent and thickness, as well as observed warming trends in Antarctica. It reports on the acceleration of mass loss from ice sheets, with projected contributions to sea level rise outpacing other factors. The findings indicate that ice sheet loss could become the dominant source of sea level rise in the coming century if current trends continue.

1. Some Developments in Climate Science
Since IPCC AR4
Prepared for the Climate Change Science Symposium
John Merrill,
URI GSO
May 6, 2011

2. Talk organization
I’ll zoom over several topics from jet stream altitude, and then
cover one finding in some detail.
There’s little rationale for this inhomogeneity.

3. Multiple topics
Since 1979, the Arctic sea ice extent has been declining at a rate
of 11% per decade. Not only did the ice extent reduce but so did
the average thickness of the sea ice, which decreased strongly; this
increases the vulnerability to further decreases.
Winter ice has decreased in thickness, and the February, 2011 the
Arctic sea ice extent was a record low.
Periods of rapid Arctic sea ice loss lead to faster warming over land
in polar regions. The exposure of low-albedo ocean waters results
in warming; the release of this heat into the atmosphere and its
transport onshore allow an extended season of microbial
decomposition of thawing peat and other organic matter.

4. Multiple topics
In AR4 the IPCC concluded that Antarctica was the only continent
where no global warming had been observed. Recent work
indicates that there has been a positive surface temperature trend
from 1957-2006 in West and East Antarctica.
The airborne fraction of CO2 may have increased recently, the
expected decrease in buffering capacity. Conflicting results from
estimates over differing time periods complicate the picture.

5. Multiple topics
The Ocean Heat Content Anomaly, OHCA, has shown a gradual
increase over the past 50 years, but analyses included substantial
decadal scale fluctuations that are larger than those seen in
model most simulations.
Recent work detecting systematic errors in the treatment of the
data have led to revised estimates, with reduced interdecadal
variability. Also, parallel analyses by different groups yield similar
results, providing corroboration.
The linear trends in the Ocean Heat Content of the upper 700 m
are 0.27± 0.04 ×1022 J/yr for the period 1955 - 2008 and 0.40±
0.05 ×1022 J/yr for the period 1969 - 2008.

6. Acceleration of mass loss from ice sheets
Rignot et al. (GRL, 2011), present mass balance observations for
Greenland and Antarctica ice sheets over two decades. The
observations are corroborated by comparison of two techniques
over the most recent 8 years.
The ice data are Surface Mass Balance estimates (snowfall minus
ablation), combined with perimeter loss (ice discharge) estimates.
Satellite data are a time series of monthly time-resolved gravity
data from the Gravity Recovery and Climate Experiment (GRACE).

7. Acceleration of mass loss from ice sheets
Data are dM/dt estimates
using Mass Budget Method
(MBM) (solid black circle) and
GRACE time-variable gravity
(solid red triangle).
Total ice sheet mass balance,
dM/dt, in Gt/yr. 1992 - 2009
for
(a) Greenland;
(b) Antarctica;
(c) the sum of Greenland
and Antarctica.
Note expanded y-axis range in
(Rignot et al. 2011, Figure 2.) (c).

8. Acceleration of mass loss from ice sheets
The agreement of the MBM and GRACE estimates is especially
good in Antarctica.

9. The acceleration rate in ice sheet mass balance, in Gt/yr2 , is
determined from a linear fit of MBM over 18 yr (black line) and
GRACE over 8 yr (red line).
The combined acceleration of ice sheet mass loss totals over 36
Gt/yr2 . This acceleration is over 3 times that for mountain glaciers
and ice caps.
The estimated contribution to sea level rise over the next 50 years
would be 15±2 cm, exceeding the impact of melting of individual
glaciers and ice caps, 8±4 cm, and thermal expansion of the
ocean, 9±3 cm.
If continued, this trend would make ice sheet loss the dominant
source of sea level rise in the upcoming century.

10. Final notes
Recall that findings published after March, 2006 are not cited or
used substantively in AR4.
Numerical models of sea ice extent significantly underestimate the
observed downward trend. I have concluded that these models will
remain unreliable until significant advances can be made.

11. Some sources
Peter Good, et al., An updated review of developments in climate
science research since the IPCC Fourth Assessment Report. [An
extended (177 page) analysis by British Met Office and affiliated
analysts, up to date to November, 2010.]
Kelly Levin and D. Tirpak, Climate Science 2008 - Major New
Discoveries. World Resource Institute “Issue Brief”, 28 pp, July,
2009.
R. vanDorland et al.,News in Climate Science since IPCC 2007:
Topics of interest in the scientific basis of climate change, KNMI,
de Bilt, November, 2009.