Tracking uncertainties in the causal chain from human activities to climate

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95537/1/grl25489.pd

Recent changes (1991-2010) in glacier mass balance and air temperature in the European Alps

AbstractWe estimate temperature sensitivity of observed mass balance for glaciers in the European Alps to compare with our earlier estimates from modelling. We treat 1961-90 as our reference period and compare mass balance for 1991-2010 with this reference period. There are eight Alpine glaciers with long enough records. The mean mass balance for the eight glaciers is close to zero for the reference period, very negative for 1991-2010 and highly negative in the exceptionally warm year 2003. Mass-balance changes are compared with 1991-2010 temperature anomalies to give an average temperature sensitivity of approximately -0.7 ± 0.2 m w.e. a-1 K-1 for the eight glaciers. There is considerable variation between individual glaciers, with higher sensitivity for western glaciers and lower sensitivity for eastern glaciers. Temperature sensitivity for the eight glaciers is strongly correlated with the standard deviation of observed mass balance, which from earlier work is known to be correlated with winter balance. The mean temperature sensitivity for observed mass balance is in reasonable agreement with values from earlier models, but changes in glacier hypsometry during 1991-2010 may have further increased observed mass loss.</jats:p

The role of aviation emissions in climate stabilization scenarios

Climate stabilization is embedded in UK and EU policy objectives and stabilization scenarios make assumptions over short and long-term emissions reductions. Air traffic, however, is increasing at 3 – 5% per year. The technological possibilities of reducing aircraft CO2 are limited and projected traffic growth overwhelms gains from fuel efficiency. MAGICC and a climate response model are used to examine the addition of aviation effects (CO2, O3, CH4, sulphate, soot and contrails) onto stabilization scenarios. Aviation makes a small but significant contribution to radiative forcing and global temperature responses. Whilst this is small globally, the necessary policy response of the three major centres of aviation (North America, Europe and the Far East) may be demanding; these emissions potentially form a large fraction of a country or region’s CO2 emissions. This may provoke further thinking over emissions trading as the way forward to incorporate international aviation emissions into Kyoto and post-Kyoto targets

from a degree-day

Accumulation at the equilibrium-line altitude of glaciers inferre

Greenhouse-gas emission targets for limiting global warming to 2°C

More than 100 countries have adopted a global warming limit of 2°C or below (relative to pre-industrial levels) as a guiding principle for mitigation efforts to reduce climate change risks, impacts and damages. However, the greenhouse gas (GHG) emissions corresponding to a specified maximum warming are poorly known owing to uncertainties in the carbon cycle and the climate response. Here we provide a comprehensive probabilistic analysis aimed at quantifying GHG emission budgets for the 2000-50 period that would limit warming throughout the twenty-first century to below 2°C, based on a combination of published distributions of climate system properties and observational constraints. We show that, for the chosen class of emission scenarios, both cumulative emissions up to 2050 and emissions levels in 2050 are robust indicators of the probability that twenty-first century warming will not exceed 2°C relative to pre-industrial temperatures. Limiting cumulative CO₂ emissions over 2000-50 to 1,000 Gt CO₂ yields a 25% probability of warming exceeding 2°C - and a limit of 1,440 Gt CO₂ yields a 50% probability - given a representative estimate of the distribution of climate system properties. As known 2000-06 CO₂ emissions were ~234 Gt CO₂ less than half the proven economically recoverable oil, gas and coal reserves can still be emitted up to 2050 to achieve such a goal. Recent G8 Communiqués envisage halved global GHG emissions by 2050, for which we estimate at 12-45% probability of exceeding 2°C - assuming 1990 as emission base year and a range of published climate sensitivity distributions. Emissions levels in 2020 are a less robust indicator, but for the scenarios considered, the probability of exceeding 2°C rises to 53-87% if global GHG emissions are still more than 25% above 2000 levels in 2020

The Potential for Sea Level Rise: new estimates from Glacier and Ice Cap area and volume distributions

Projections of sea-level rise from mountain glaciers and ice caps for the next century and beyond should be based on an assessment of the ice available for melting. Projections to date are based on all regions except Greenland and Antarctica (the latter are considered separately by the IPCC), yet no sound estimates for the appropriate volume of ice and its potential for sea level rise are evident in the literature. An ice cap data set is compiled allowing the separate treatment of glacier area coverage data. Glacier inventory data are comprehensive enough in some regions to allow the estimation of glacier size distributions. The differences in the distributions are related to a metric of the regional topographic variability, allowing glacier size distributions to be estimated on a 1o latitude longitude grid of cells containing glaciers. Appropriate volume-area scaling for glaciers and for ice caps gives global estimates of glacier and ice cap volumes by size class. This leads to an estimate of the total ice volume of 0.087 ± 0.010 106 km3 and a sea level rise equivalent of 0.241 ± 0.026 m. The glaciers and ice caps contribute 41% and 59% to these estimates respectively. These values are based on data sets compiled during several decades, mainly in the second half of the 20th Century. We compare our results to published results that include the glaciers and icecaps at the margins of the Greenland and Antarctic ice sheet