It ain't necessarily so on sea rise

At the same time relatively warm ocean water penetrates deep under the ice sheet, pushing back the grounding line of glaciers, enabling an increase in their outflow. The result: land based ice is simultaneously attacked from above and below, further accelerating SLR. There can be no doubt that the cryosphere, particularly in polar regions, is in serious and irreversible decline.

Hansen et al

When predicting SLR this century, the IPCC accepts the broad view that mean global sea level will rise ~90cm by 2100. It does not accept "outlaying values" (5m) provided in an essay by Hansen (2005) based on paleo-climate research of sea level during the Eemian interglacial. That research shows that with average global surface temperature 2°C above the pre-industrial and when atmospheric CO2 concentration was around 280 ppm, mean global SLR during the Eemian maximumwas 5m-9m higher than at present.

More recently, Hansen has shown that mean global SLR in the order of 5m by 2100 is supported by both paleo-climate and observed trends showing decadal doubling of ice mass loss from polar ice sheets. Hansen shows

that were that trend to persist, sea level would indeed rise ~5m. by 2100. Based on polar ice mass loss in the year 2000, actual loss from the GIS to 2009 had more than doubled in less than a decade.

When challenged on the basis that SLR could not be so rapid in such a short period (~100 years), Hansen (2005) draws attention to Pulse 1A during the Holocene when sea level rose at a rate of ~ +4m per century over 5 consecutive centuries.

Yet the analyses of eminent scientists which fall outside majority consensus conclusions published by the IPCC, are seemingly not considered sufficiently "reliable" to base its own prognosis of sea level rise this century. Even so, a growing number of scientists are coming to the view that mean global sea level rise, well in excess of 2m, is both possible and increasingly likely by 2100.

Hansen et al (2016) and 18 eminent co-authors point out that polar ice loss results in cooling of ocean surface water, while tropical warming continues, increasing surface energy imbalance. This increases the incidence and severity of destructive storms, far more severe than this, pushing sea level even higher where they occur, increasing the threat to coastal population centres, causing coastal erosion and flooding of low lying land.

Summary

The IPCC 5AR prognosis for sea level rise over the next century appears to be a dangerous underestimate for policy makers because it:

• Relies on CMIP5 which underestimates present and future Arctic warming
• Underestimates the Global Warming Potential of CH4
• Ignores the effect of carbon emissions associated with permafrost degradation on Arctic amplification
• Miscalculates the rate of albedo reduction (due to aerosols, sea ice loss and Arctic amplification) and its effect on polar ice
• Underestimates the rate of ocean warming, particularly bottom water and its effects on polar ice sheets
• Ignores analyses by Hansen et al indicating multi metre sea level rise and severe storm surges before 2100.

Conclusion: