Michael W. Wara

Regional climate shifts caused by gradual global cooling in the pliocene epoch

The Earths climate has undergone a global transition over the past four million years, from warm conditions with global surface temperatures about 3 °C warmer than today, smaller ice sheets and higher sea levels to the current cooler conditions. Tectonic changes and their influence on ocean heat transport have been suggested as forcing factors for that transition, including the onset of significant Northern Hemisphere glaciation ∼2.75 million years ago, but the ultimate causes for the climatic changes are still under debate. Here we compare climate records from high latitudes, subtropical regions and the tropics, indicating that the onset of large glacial/interglacial cycles did not coincide with a specific climate reorganization event at lower latitudes. The regional differences in the timing of cooling imply that global cooling was a gradual process, rather than the response to a single threshold or episodic event as previously suggested. We also find that high-latitude climate sensitivity to variations in solar heating increased gradually, culminating after cool tropical and subtropical upwelling conditions were established two million years ago. Our results suggest that mean low-latitude climate conditions can significantly influence global climate feedbacks.

Is the global carbon market working

The Clean Development Mechanism can be viewed not only as a market, but also as a subsidy and a political mechanism. Michael Wara argues that it has been most effective, so far, in achieving its political goals.

Interlaboratory comparison study of Mg/Ca and Sr/Ca measurements in planktonic foraminifera for paleoceanographic research

Thirteen laboratories from the USA and Europe participated in an intercomparison study of Mg/Ca and Sr/Ca measurements in foraminifera. The study included five planktonic species from surface sediments from different geographical regions and water depths. Each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples. Analysis of solutions of known Mg/Ca and Sr/Ca ratios showed that the intralaboratory instrumental precision is better than 0.5% for both Mg/Ca and Sr/Ca measurements, regardless whether ICP-OES or ICP-MS is used. The interlaboratory precision on the analysis of standard solutions was about 1.5% and 0.9% for Mg/Ca and Sr/Ca measurements, respectively. These are equivalent to Mg/Ca-based temperature repeatability and reproducibility on the analysis of solutions of ±0.2°C and ±0.5°C, respectively. The analysis of foraminifera suggests an interlaboratory variance of about ±8% (%RSD) for Mg/Ca measurements, which translates to reproducibility of about ±2–3°C. The relatively large range in the reproducibility of foraminiferal analysis is primarily due to relatively poor intralaboratory repeatability (about ±1–2°C) and a bias (about 1°C) due to the application of different cleaning methods by different laboratories. Improving the consistency of cleaning methods among laboratories will, therefore, likely lead to better reproducibility. Even more importantly, the results of this study highlight the need for standards calibration among laboratories as a first step toward improving interlaboratory compatibility.

Late Miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing.

Deep-time palaeoclimate studies are vitally important for developing a complete understanding of climate responses to changes in the atmospheric carbon dioxide concentration (that is, the atmospheric partial pressure of CO2, pCO2). Although past studies have explored these responses during portions of the Cenozoic era (the most recent 65.5 million years (Myr) of Earth history), comparatively little is known about the climate of the late Miocene (∼12–5 Myr ago), an interval with pCO2 values of only 200–350 parts per million by volume but nearly ice-free conditions in the Northern Hemisphere and warmer-than-modern temperatures on the continents. Here we present quantitative geochemical sea surface temperature estimates from the Miocene mid-latitude North Pacific Ocean, and show that oceanic warmth persisted throughout the interval of low pCO2 ∼12–5 Myr ago. We also present new stable isotope measurements from the western equatorial Pacific that, in conjunction with previously published data, reveal a long-term trend of thermocline shoaling in the equatorial Pacific since ∼13 Myr ago. We propose that a relatively deep global thermocline, reductions in low-latitude gradients in sea surface temperature, and cloud and water vapour feedbacks may help to explain the warmth of the late Miocene. Additional shoaling of the thermocline after 5 Myr ago probably explains the stronger coupling between pCO2, sea surface temperatures and climate that is characteristic of the more recent Pliocene and Pleistocene epochs.

The pacemaker always rings twice

We generated new, long, high-resolution, climate proxy records from Deep Sea Drilling Project (DSDP) Sites 607 and 609 in the subpolar North Atlantic over the interval 225–970 ka, which have pronounced variability at periods f > 1/7 kyr) variance in our North Atlantic climate proxy records is shown, using bispectral and cross-bispectral methods, to be explainable as harmonics and/or combination tones of orbital-scale climatic variability of the North Atlantic region itself. Thus the timing and amplitude of high-frequency climate change in the North Atlantic region appears to be a nonlinear function of variations in high-latitude climate at Milankovitch frequencies.

The evolution of the equatorial thermocline and the early Pliocene El Padre mean state

The tropical Pacific thermocline strength, depth, and tilt are critical to tropical mean state and variability. During the early Pliocene (~3.5 to 4.5 Ma), the Eastern Equatorial Pacific (EEP) thermocline was deeper and the cold tongue was warmer than today, which resulted in a mean state with a reduced zonal sea surface temperature gradient or El Padre. However, it is unclear whether the deep thermocline was a local feature of the EEP or a basin-wide condition with global implications. Our measurements of Mg/Ca of Globorotalia tumida in a western equatorial Pacific site indicate Pliocene subsurface temperatures warmer than today; thus, El Padre included a basin-wide thermocline that was relatively warm, deep, and weakly tilted. At ~4 Ma, thermocline steepening was coupled to cooling of the cold tongue. Since ~4 Ma, the basin-wide thermocline cooled/shoaled gradually, with implications for thermocline feedbacks in tropical dynamics and the interpretation of TEX86-derived temperatures.

An economic perspective on the EPA's Clean Power Plan

Cross-state coordination key to cost-effective CO2 reductions In June, the Obama Administration unveiled its proposal for a Clean Power Plan, which it estimates would reduce carbon dioxide (CO2) emissions from existing U.S. power plants 30% below 2005 levels by 2030 (see the chart). Power plant emissions have declined substantially since 2005, so the plan is seeking reductions of about 18% from current levels. Electricity generation accounts for about 40% of U.S. CO2 emissions.

Carbon markets: Effective policy?

In Their Policy Forum “Carbon market lessons and global policy outlook” (21 March, p. [1316][1]), R. G. Newell and his colleagues present an optimistic—but ultimately misleading—picture of existing carbon markets. Citing the expanded use of carbon markets, Newell et al. use economic theory

California’s energy and climate policy: A full plate, but perhaps not a model policy

California is a leader among states in its efforts to cut greenhouse gas emissions. Under the California Global Warming Solutions Act of 2006 (Assembly Bill 32), the state has set itself on a course to reduce its greenhouse gas emissions to 1990 levels by the year 2020. In addition to its cap-and-trade program, California aims to accomplish this objective via a large assortment of complementary and overlapping policies. To a significant degree, cap-and-trade is a market-based “dessert” that follows a multicourse menu of other regulatory initiatives aimed at cutting emissions. The reduced cost-effectiveness, political costs, and regulatory costs associated with this approach make it unlikely to form a suitable model for states in which political commitment to climate action is more limited or regulatory capacity is not as great as in California.

Building an Effective Climate Regime While Avoiding Carbon and Energy Stalemate

The world needs a new approach to achieving international progress on climate change. Despite prodigious diplomatic efforts over two decades aimed at limiting emissions of climate change pollutants, relatively little in the way of effective global governance has been achieved. In Part 1, I argue that this is due to a narrow legal, economic, and political focus on the hardest part of the climate change problem – energy related carbon dioxide emissions. Part 2 explains key scientific developments over the past two decades and how these have reshaped the scientific view of human impacts on climate. Studies aimed at resolving the remaining uncertainties in climate projections have resulted in a dramatically improved understanding of the importance of short-lived climate pollutants in causing current and medium-term climate change. In Part 3, I argue that such a shift in focus to short-lived climate pollutants could produce more effective outcomes. In Part 4, I provide an account of how short-lived climate pollutants might form a path toward more comprehensive international greenhouse gas limits in the future. In the long run, a multilateral agreement limiting energy related carbon emissions is essential to avoiding the worst impacts of climate change. But simply repeating the failed strategies of the last twenty years is unlikely to accomplish that end. This article aims to provide a plausible path forward to deep cooperation that is consistent with current scientific knowledge, technical ability, and international law and relations theory.