The danger of overvaluing methane’s influence on future climate change

Minimizing the future impacts of climate change requires reducing the greenhouse gas (GHG) load in the atmosphere. Anthropogenic emissions include many types of GHG’s as well as particulates such as black carbon and sulfate aerosols, each of which has a different effect on the atmosphere, and a different atmospheric lifetime. Several recent studies have advocated for the importance of short timescales when comparing the climate impact of different climate pollutants, placing a high relative value on short-lived pollutants, such as methane (CH₄) and black carbon (BC) versus carbon dioxide (CO₂). These studies have generated confusion over how to value changes in temperature that occur over short versus long timescales. We show the temperature changes that result from exchanging CO₂ for CH₄ using a variety of commonly suggested metrics to illustrate the trade-offs involved in potential carbon trading mechanisms that place a high value on CH₄ emissions. Reducing CH₄ emissions today would lead to a climate cooling of approximately ~0.5 °C, but this value will not change greatly if we delay reducing CH₄ emissions by years or decades. This is not true for CO₂, for which the climate is influenced by cumulative emissions. Any delay in reducing CO₂ emissions is likely to lead to higher cumulative emissions, and more warming. The exact warming resulting from this delay depends on the trajectory of future CO₂ emissions but using one business-as usual-projection we estimate an increase of 3/4 °C for every 15-year delay in CO₂ mitigation. Overvaluing the influence of CH₄ emissions on climate could easily result in our “locking” the earth into a warmer temperature trajectory, one that is temporarily masked by the short-term cooling effects of the CH₄ reductions, but then persists for many generations.     

Impact of the winter North-Atlantic weather regimes on subtropical sea-surface height variability

Interannual variability of subtropical sea-surface-height (SSH) anomalies, estimated by satellite and tide-gauge data, is investigated in relation to wintertime daily North-Atlantic weather regimes. Sea-level anomalies can be viewed as proxies for the subtropical gyre intensity because of the intrinsic baroclinic structure of the circulation. Our results show that the strongest correlation between SSH and weather regimes is found with the so-called Atlantic-Ridge (AR) while no significant values are obtained for the other regimes, including those related to the North Atlantic Oscillation (NAO), known as the primary actor of the Atlantic dynamics. Wintertime AR events are characterized by anticyclonic wind anomalies off Europe leading to a northward shift of the climatological wind-stress curl. The latter affects subtropical SSH annual variability by altered Sverdrup balance and ocean Rossby wave dynamics propagating westward from the African coast towards the Caribbean. The use of a simple linear planetary geostrophic model allows to quantify those effects and confirms the primary importance of the winter season to explain the largest part of SSH interannual variability in the Atlantic subtropical gyre. Our results open new perspectives in the comprehension of North-Atlantic Ocean variability emphasizing the role of AR as a driver of interannual variability at least of comparable importance to NAO.     

Funding low-carbon investments in the absence of a carbon tax

Introducing a carbon tax is difficult, partly because it suggests that current generations have to make sacrifices for the benefit of future generations. However, the climate change externality could be corrected without such a sacrifice. It is possible to set a carbon value, and use it to create ‘carbon certificates’ that can be accepted as part of commercial banks’ legal reserves. These certificates can be distributed to low-carbon projects, and be exchanged by investors against concessional loans, reducing capital costs for low-carbon projects. As the issuance of carbon certificates would increase the quantity of money, it will either lead to accelerated inflation or induce the Central Bank to raise interest rates. Low-carbon projects will thus have access to cheaper loans at the expense of either ‘regular’ investors (in case of higher interest rates) or of lenders and depositors (in case of accelerated inflation). Within this scheme, mitigation expenditures are compensated by a reduction in regular investments, so that immediate consumption is maintained. It uses future generation wealth to pay for a hedge against climate change. This framework is not as efficient as a carbon tax but is politically easier to implement and represents an interesting step in the trajectory towards a low-carbon economy.     

Pattern scaling: Its strengths and limitations,and an update on the latest model simulations

We review the ideas behind the pattern scaling technique, and focus on its value and limitations given its use for impact assessment and within integrated assessment models. We present estimates of patterns for temperature and precipitation change from the latest transient simulations available from the Coupled Model Inter-comparison Project Phase 5 (CMIP5), focusing on multi-model mean patterns, and characterizing the sources of variability of these patterns across models and scenarios. The patterns are compared to those obtained from the previous set of experiments, under CMIP3. We estimate the significance of the emerging differences between CMIP3 and CMIP5 results through a bootstrap exercise, while also taking into account the fundamental differences in scenario and model ensemble composition. All in all, the robustness of the geographical features in patterns of temperature and precipitation, when computed as multi-model means, is confirmed by this comparison. The intensity of the change (in both the warmer and cooler areas with respect to global temperature change, and the drier and wetter regions) is overall heightened per degree of global warming in the ensemble mean of the new simulations. The presence of stabilized scenarios in the new set of simulations allows investigation of the performance of the technique once the system has gotten close to equilibrium. Overall, the well established validity of the technique in approximating the forced signal of change under increasing concentrations of greenhouse gases is confirmed.     

THE EIGHTIETH BIRTHDAY OF AN EMINENT WORLD CARTOGRAPHER

The multifaceted career and contributions of Professor Konstantin A. Salishchev, Chair of the Moscow University Department of Cartography and eminent world cartographer, are celebrated on the occasion of his eightieth birthday. These contributions include but are not restricted to: scholarly and administrative work in upgrading national atlas cartography worldwide, improvement of the quality of maps and cartographic instruction in higher education, publication of numerous excellent cartographic texts, formulation of the concept of the “cartographic method of research,” and promotion of international cooperation among cartographers and geographers through active participation and leadership in numerous world professional organizations. From the Russian original by I. D. Papanin, G. I. Rychagov, and A. F. Treshnikov.     

Are peatlands in different states with respect to their thermodynamic behaviour? A simple test of peatland energy and entropy budgets

Whilst all ecosystems must obey the second law of thermodynamics, these physical bounds and controls on ecosystem evolution and development are largely ignored across the ecohydrological literature. To unravel the importance of these underlying restraints on ecosystem form and function, and their power to inform our scientific understanding, we have calculated the entropy budget of a range of peat ecosystems. We hypothesize that less disturbed peatlands are ‘near equilibrium’ with respect to the second law of thermodynamics and thus respond to change by minimizing entropy production. This ‘near equilibrium’ state is best achieved by limiting evaporative losses. Alternatively, peatlands ‘far-from-equilibrium’ respond to a change in energy inputs by maximizing entropy production which is best achieved by increasing evapotranspiration. To test these alternatives this study examined the energy balance time series from seven peatlands across a disturbance gradient. We estimate the entropy budgets for each and determine how a change in net radiation (ΔR_n) was transferred to a change in latent heat flux (ΔλE). The study showed that: (i) The transfer of net radiation to latent heat differed significantly between peatlands. One group transferred up to 64% of the change in net radiation to a change in latent heat flux, while the second transferred as little as 27%. (ii) Sites that transferred the most energy to latent heat flux were those that produced the greatest entropy. The study shows that an ecosystem could be ‘near equilibrium’ rather than ‘far from equilibrium’.