Protecting the Arctic
Supplementary written evidence submitted by the Met Office
1. This memorandum provides an update to previous Met Office evidence to the Environmental Audit Committee. Our earlier evidence pointed to the expectation that Cryosat-2 would provide important Arctic-wide observations of sea-ice thickness; the preliminary results are now available along with their implications for the current state of the Arctic.
2. Recent estimates of Arctic sea ice volume using the CryoSat-2 satellite combined with earlier estimates using the ICESat satellite show that over the period 2003-2012 ice volume in the summer Arctic has declined substantially. This result is consistent with independent estimates from PIOMAS, which is a model-based estimate constrained by available observations (but not directly by IceSat/CryoSat-2).
3. The changes in observed sea-ice volume only extends over a few years and cannot in isolation be interpreted as representative of a long term trend. In addition, evidence of the continuing influence of weather patterns has again been seen in the rapid loss of sea-ice cover this August. Nevertheless it is important not to allow periodic and short term natural variations (down or up) to detract from the longer term trend of declining sea ice over recent and coming decades and the increasing fragility of the system. The extrapolation of short-term trends in ice volume is not a reliable way to predict when the Arctic will be seasonally ice free as negative feedbacks and changing weather patterns may slow the rate of ice loss.
4. Climate models represent our best understanding of the physics of the ocean, atmosphere and sea ice and continue to provide the most reliable tool to estimate future behaviour. Indeed, the Met Office considers that the IceSat/CryoSat-2 observations of ice volume loss during the beginning of the 21st Century are broadly consistent with a number of climate models. However, it is worth noting that climate models can show a period of recovery in ice volume following periods of large ice volume loss.
As the observational record of ice volume is continued, detailed comparisons will be made to evaluate and improve the climate models and to update assessments of the future evolution of the Arctic.
31 August 2012