Can ozone depletion and global warming interact to produce rapid climate change?

The atmosphere displays modes of variability whose structures exhibit a strong longitudinally symmetric (annular) component that extends from the surface to the stratosphere in middle and high latitudes of both hemispheres. In the past 30 years, these modes have exhibited trends that seem larger than their natural background variability, and may be related to human influences on stratospheric ozone and/or atmospheric greenhouse gas concentrations. The pattern of climate trends during the past few decades is marked by rapid cooling and ozone depletion in the polar lower stratosphere of both hemispheres, coupled with an increasing strength of the wintertime westerly polar vortex and a poleward shift of the westerly wind belt at the earth's surface. Annular modes of variability are fundamentally a result of internal dynamical feedbacks within the climate system, and as such can show a large response to rather modest external forcing. The dynamics and thermodynamics of these modes are such that strong synergistic interactions between stratospheric ozone depletion and greenhouse warming are possible. These interactions may be responsible for the pronounced changes in tropospheric and stratospheric climate observed during the past few decades. If these trends continue, they could have important implications for the climate of the 21st century.

Climate change is affecting altitudinal migrants and hibernating species

Calendar date of the beginning of the growing season at high altitude in the Colorado Rocky Mountains is variable but has not changed significantly over the past 25 years. This result differs from growing evidence from low altitudes that climate change is resulting in a longer growing season, earlier migrations, and earlier reproduction in a variety of taxa. At our study site, the beginning of the growing season is controlled by melting of the previous winter's snowpack. Despite a trend for warmer spring temperatures the average date of snowmelt has not changed, perhaps because of the trend for increased winter precipitation. This disjunction between phenology at low and high altitudes may create problems for species, such as many birds, that migrate over altitudinal gradients. We present data indicating that this already may be true for American robins, which are arriving 14 days earlier than they did in 1981; the interval between arrival date and the first date of bare ground has grown by 18 days. We also report evidence for an effect of climate change on hibernation behavior; yellow-bellied marmots are emerging 38 days earlier than 23 years ago, apparently in response to warmer spring air temperatures. Migrants and hibernators may experience problems as a consequence of these changes in phenology, which may be exacerbated if climate models are correct in their predictions of increased winter snowfall in our study area. The trends we report for earlier formation of permanent snowpack and for a longer period of snow cover also have implications for hibernating species.

Characteristics of the deep ocean carbon system during the past 150,000 years: ΣCO2 distributions, deep water flow patterns, and abrupt climate change

Studies of carbon isotopes and cadmium in bottom-dwelling foraminifera from ocean sediment cores have advanced our knowledge of ocean chemical distributions during the late Pleistocene. Last Glacial Maximum data are consistent with a persistent high-ΣCO2 state for eastern Pacific deep water. Both tracers indicate that the mid-depth North and tropical Atlantic Ocean almost always has lower ΣCO2 levels than those in the Pacific. Upper waters of the Last Glacial Maximum Atlantic are more ΣCO2-depleted and deep waters are ΣCO2-enriched compared with the waters of the present. In the northern Indian Ocean, δ13C and Cd data are consistent with upper water ΣCO2 depletion relative to the present. There is no evident proximate source of this ΣCO2-depleted water, so I suggest that ΣCO2-depleted North Atlantic intermediate/deep water turns northward around the southern tip of Africa and moves toward the equator as a western boundary current. At long periods (>15,000 years), Milankovitch cycle variability is evident in paleochemical time series. But rapid millennial-scale variability can be seen in cores from high accumulation rate series. Atlantic deep water chemical properties are seen to change in as little as a few hundred years or less. An extraordinary new 52.7-m-long core from the Bermuda Rise contains a faithful record of climate variability with century-scale resolution. Sediment composition can be linked in detail with the isotope stage 3 interstadials recorded in Greenland ice cores. This new record shows at least 12 major climate fluctuations within marine isotope stage 5 (about 70,000–130,000 years before the present).

Abrupt climate change and thermohaline circulation: Mechanisms and predictability

The ocean's thermohaline circulation has long been recognized as potentially unstable and has consequently been invoked as a potential cause of abrupt climate change on all timescales of decades and longer. However, fundamental aspects of thermohaline circulation changes remain poorly understood.

Sensitivity and rapidity of vegetational response to abrupt climate change

Rapid climate change characterizes numerous terrestrial sediment records during and since the last glaciation. Vegetational response is best expressed in terrestrial records near ecotones, where sensitivity to climate change is greatest, and response times are as short as decades.

Recommendations for Creating and Implementing Climate Change Mitigation Strategies for Municipalities

The effects of climate change are beginning to show themselves globally and not enough is being done to counteract these changes. Institutional action is a necessity, and municipalities have an opportunity to fill this void by developing mitigation strategies that will reduce greenhouse gas emissions. This report critically reviews the municipal climate action plans for Portland, Oregon; Boulder, Colorado; and Toronto, Ontario and provides recommendations for other municipalities who wish to create and implement climate change mitigation plans.

An Assessment of US Progress towards its Pledge on Climate Change Mitigation. CEPS ECP Report No. 12, 15 October 2012

In 2009, President Obama pledged that, by 2020, the United States would achieve reductions in greenhouse gas emissions of 17% from 2005 levels. With the failure of Congress to adopt comprehensive climate legislation in 2010, the feasibility of the pledge was put in doubt. However, we find that the United States is near to reaching this goal: the country is currently on course to achieve reductions of 16.3% from 2005 levels in 2020. Three factors contribute to this outcome: greenhouse gas regulations under the Clean Air Act, secular trends including changes in relative fuel prices and energy efficiency and sub-national efforts. Perhaps even more surprising, domestic emissions are probably lower than would have been the case if the Waxman-Markey cap-and-trade proposal had become law in 2010. At this point, however, the United States is expected to fail to meet its financing commitments under the Copenhagen Accord for 2020.

EU Policy on Climate Change Mitigation since Copenhagen and the Economic Crisis. CEPS Working Document No. 380, 5 March 2013

The EU has long assumed leadership in advancing domestic and international climate change policy. While pushing its partners in international negotiations, it has led the way in implementing a host of domestic measures, including a unilateral and legally binding target, an ambitious policy on renewable energy and a strategy for low-carbon technology deployment. The centrepiece of EU policy, however, has been the EU Emissions Trading System (ETS), a cap-and-trade programme launched in 2005. The ETS has been seen as a tool to ensure least-cost abatement, drive EU decarbonisation and develop a global carbon market. After an initial review and revision of the ETS, to come into force in 2013, there was a belief that the new ETS was ‘future-proof’, meaning able to cope with the temporary lack of a global agreement on climate change and individual countries’ emission ceilings. This confidence has been shattered by the simultaneous ‘failure’ of Copenhagen to deliver a clear prospect of a global (top-down) agreement and the economic crisis. The lack of prospects for national caps at the international level has led to a situation whereby many member states hesitate to pursue ambitious climate change policies. In the midst of this, the EU is assessing its options anew. A number of promising areas for international cooperation exist, all centred on the need to ‘raise the ambition level’ of GHG emission reductions, notably in aviation and maritime, short-lived climate pollutions, deforestation, industrial competitiveness and green growth. Public policy issues in the field of technology and its transfer will require more work to identify real areas for cooperation.