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    Researchers say air temperatures here in northwest Canada, in Siberia and elsewhere in the Arctic have risen more than 2.5 C (4.5 F) since 1970 — much faster than the global average. The summer thaw is reaching deeper into frozen soil, at a rate of 4 centimeters (1.5 inches) a year, and a further 7 C (13 F) temperature rise is possible this century, says the authoritative, U.N.-sponsored Intergovernmental Panel on Climate Change (IPCC).

    In 2007, air monitors detected a rise in methane concentrations in the atmosphere, apparently from far northern sources. Russian researchers in Siberia expressed alarm, warning of a potential surge in the powerful greenhouse gas, additional warming of several degrees, and unpredictable consequences for Earth’s climate.

    Others say massive seeps of methane might take centuries. But the Russian scenario is disturbing enough to have led six U.S. national laboratories last year to launch a joint investigation of rapid methane release. And IPCC Chairman Rajendra Pachauri in July asked his scientific network to focus on “abrupt, irreversible climate change” from thawing permafrost.

    The data will come from teams like one led by Scott Dallimore, who with Bowen and others pitched tents here on the remote, boggy fringe of North America, 2,200 kilometers (1,400 miles) from the North Pole, to learn more about seeps in the 25,000 lakes of this vast river delta.



    Phase 4 (2009-2016) has seen a major shift in viewpoint of published papers: 30 papers favor aspects of the EAH, 6 papers oppose it, and 5 are in the middle. Most of the phase 4 papers that oppose the hypothesis or are ‘in the middle’ are based on modeling studies. Many of the 30 supporting papers are broad-scale compilations of archaeological and paleoecological evidence:
    * The average GHG trends from 7 previous interglaciations show CO2 and CH4 decreases, in contrast to the late Holocene increases;
    * Interglacial stage 19, the closest Holocene analog, shows decreases in CH4 and CO2, and the CO2 decrease closely matches the 2003 EAH prediction;
    * CH4 emissions from Asian rice paddies account for 70% of the observed CH4 rise from 5000 to 1000 years ago
    * historical data show that early per-capita land use was at least 4 times larger than assumed in several phase-3 land use simulations
    * a recent land use simulation based on historical evidence accounts for more than half the CO2 anomaly originally proposed in the EAH;
    * pollen evidence shows nearly complete deforestation in north-central Europe before the industrial era began;
    * δD and δ18O trends show anomalous late Holocene warmth compared to cooling trends in prior interglaciations, in agreement with A-OGCM simulations of the warming effect of the anthropogenic CO2 and CH4 trends.



    Between 1901 and 2010, global sea levels rose by 0.19±0.02m, albeit at varying rates and spatial distribution (Church et al. 2013) – these past values (including their uncertainty) are potentially much smaller than those associated with future projections. Whether this precise trend will continue is uncertain, but scientists are confident that sea-levels will continue to rise and accelerate due to global warming

    My background is partly in geology, so I often recall the well-known quote referring to Earth’s history ‘the present is the key to the past’ (Hutton / Lyell). In sea-level science however it might be the other way around: ‘the past is the key to the present’. Kopp et al. (2016) recently found that from the late in the 20th century sea-levels have risen faster than in any of the previous 27 centuries. Further back in time again, sea-levels have risen at much faster rates during the end of the last ice age. Past rates of change, if used wisely, provide potential constraints of future projections, together with the many semi-empirical approaches to project future sea-level rise (e.g. Rahmstorf, 2007) which are typically greater in magnitude than those from process based models. Hybrid approaches have also been undertaken (e.g. Moore et al. 2013, Mengel et al. 2016). Scientific knowledge input into process based models has much improved, reducing uncertainty of known science for some components of sea-level rise (e.g. steric changes), but when considering other components (e.g. ice melt from ice sheets, terrestrial water contribution) science is still emerging, and uncertainties remain high.

    Still, our understanding has a wide range of projections, particularly for high emissions scenarios as Jevrejeva et al. (2014) illustrates. Given emerging knowledge and changes in uncertainty, this leads me to the question, what are we adapting to, and when could this occur? Is it about 1m of rise by 2100? Or 1.4m?

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