Impatti, adattamento e vulnerabilita Le cause e le responsabilita dei cambiamenti climatici sono state trattate sul numero di ottobre della rivista Cda. Approfondiamo l’argomento presentando il documento: “Cambiamenti climatici 2007: impatti, adattamento e vulnerabilita” votato ad aprile 2007 dal secondo gruppo di lavoro del Comitato Intergovernativo sui Cambiamenti Climatici (Intergovernmental Panel on Climate Change). Si tratta del secondo di tre documenti che compongono il quarto rapporto sui cambiamenti climatici.

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Climate Change 2007: Impacts, Adaptation and Vulnerability.

We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level ~14.5 ka.

https://science.sciencemag.org/content/sci/325/5941/710.full.pdf

The Last Glacial Maximum.

▶ Addresses a wide range of timely environment, economic and energy topics ▶ A forum to review, analyze and stimulate the development, testing and implementation of mitigation and adaptation strategies at regional, national and global scales ▶ Contributes to real-time policy analysis and development as national and international policies and agreements are discussed and promulgated ▶ 94% of authors who answered a survey reported that they would definitely publish or probably publish in the journal again

Mitigation and Adaptation Strategies for Global Change

Fire is a worldwide phenomenon that appears in the geological record soon after the appearance of terrestrial plants. Fire influences global ecosystem patterns and processes, including vegetation distribution and structure, the carbon cycle, and climate. Although humans and fire have always coexisted, our capacity to manage fire remains imperfect and may become more difficult in the future as climate change alters fire regimes. This risk is difficult to assess, however, because fires are still poorly represented in global models. Here, we discuss some of the most important issues involved in developing a better understanding of the role of fire in the Earth system.

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Fire in the Earth System

This chapter assesses long-term projections of climate change for the end of the 21st century and beyond, where the forced signal depends on the scenario and is typically larger than the internal variability of the climate system. Changes are expressed with respect to a baseline period of 1986-2005, unless otherwise stated.

Chapter 12 - Long-term climate change: Projections, commitments and irreversibility

Special supplement to the Bulletin of the American Meteorological Society vol.94, No. 8, August 2013

[The Arctic] Greenland Ice Sheet [in “State of the Climate in 2012”]

N2O is a greenhouse gas that it is responsible for increased radiative forcing of the climate system. In addition to this, it is primarily destroyed in the stratosphere providing an important source of NOx, which in turn plays an important role in ozone depletion. Large uncertainties remain as to the actual strength of the individual sources of N2O. Knowledge of the historical record, of the temporal evolution of N2O emissions, can provide insight on how its sources and sinks altered during the industrial period. Data from air trapped in firn enables us to better determine the source/sink strength emissions over time.

Constraining N2O emissions over the last century by firn air isotope measurements in both hemispheres

Here, we present high-resolution stable isotope records from ODP Site 1264 in the
South-Eastern Atlantic Ocean, which resolve the latest Oligocene to early Miocene
(23.7–18.9 Ma) climate changes. Using an inverse modelling technique, we decom-
posed the oxygen isotope record into temperature and ice volume and found that the
Antarctic ice sheet expanded during distinct episodes (e.g., Mi zones) of low short-term
(∼100-kyr) eccentricity forcing, which occur two to four long-term (400-kyr) eccentricity
cycles apart. We argue that a non-linear mechanism, such as the merging of (several)
large East Antarctic ice sheets, caused the build-up of a larger ice sheet. During the
termination phases of these larger ice sheets, on the contrary, we find a more linear response
of ice-sheet variability to orbital forcing and climate became highly sensitive to
the ∼100-kyr eccentricity cycle. At the Oligocene-Miocene transition the model output
indicates a decrease in Northern Hemisphere temperatures such that a small ice cap
could develop on Greenland. This supports the hypothesis of a threshold response for
the development of Northern Hemisphere land ice to decreasing pCO2.

/pdf/dynamics-of-100-kyr-glacial-cycles-during-the-early-miocene-22jbv2n98a.pdf

Dynamics of ~100-kyr glacial cycles during the early Miocene

Arctic Report Card 2020: Greenland Ice Sheet

The climate sensitivity parameter S is defined as the equilibrium change in global annual mean surface temperature ∆T per radiative forcing ∆R, S= ∆T/∆R. We here combine a data set of radiative forcing ∆R of greenhouse gases and albedo changes (Kohler et al., 2010) with an estimate of ∆T based on the deconvolution of benthic δ18O into sealevel and temperature (Bintanja et al., 2005) for the last 800 kyr.
We show how S varies depending on the radiative forcing considered, e.g. if only ∆R of CO2 or ∆R of CO2+CH4+N2O or additionally ∆R of the albedo changes are taken into account. Furthermore we find, that for the LGM all calculated S, independent on the considered forcing ∆R is about 10-15% smaller than if calculated for the whole 800 kyr time window. We propose that this difference between the rather stable climate of the LGM and the whole 800 kyr is caused by transient effects and the state dependency of S. We identify based on thresholds in temporal changes in ∆T and ∆R relatively stable climates and separate the transient effect from state dependency in S.
In a final application it is shown how the state dependency of S and assumptions on various slow and fast feedbacks are important for the functional relationship between ∆T and CO2 for the range in CO2 observed in the past 800 kyr and proposed in the future (2×CO2).

/pdf/the-climate-sensitivity-parameter-during-the-last-800-kyr-586lopsbed.pdf

R. S. W. van de Wal

Papers

[The Arctic] Greenland Ice Sheet [in “State of the Climate in 2012”]

Constraining N2O emissions over the last century by firn air isotope measurements in both hemispheres

Dynamics of ~100-kyr glacial cycles during the early Miocene

Arctic Report Card 2020: Greenland Ice Sheet

The climate sensitivity parameter during the last 800 kyr - offsets due to transient effects and state dependency