John Andrew Dykema

Achieving Climate Change Absolute Accuracy in Orbit

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission will provide a calibration laboratory in orbit for the purpose of accurately measuring and attributing climate change. CLARREO measurements establish new climate change benchmarks with high absolute radiometric accuracy and high statistical confidence across a wide range of essential climate variables. CLARREOs inherently high absolute accuracy will be verified and traceable on orbit to Systeme Internationale (SI) units. The benchmarks established by CLARREO will be critical for assessing changes in the Earth system and climate model predictive capabilities for decades into the future as society works to meet the challenge of optimizing strategies for mitigating and adapting to climate change. The CLARREO benchmarks are derived from measurements of the Earths thermal infrared spectrum (5–50 μm), the spectrum of solar radiation reflected by the Earth and its atmosphere (320–2300 nm), and radio occultation refractivity from which...

Incorporating Climate Uncertainty into Estimates of Climate Change Impacts

Quantitative estimates of the impacts of climate change on economic outcomes are important for public policy. We show that the vast majority of estimates fail to account for well-established uncertainty in future temperature and rainfall changes, leading to potentially misleading projections. We reexamine seven well-cited studies and show that accounting for climate uncertainty leads to a much larger range of projected climate impacts and a greater likelihood of worst-case outcomes, an important policy parameter. Incorporating climate uncertainty into future economic impact assessments will be critical for providing the best possible information on potential impacts.

Absolute, spectrally-resolved, thermal radiance: a benchmark for climate monitoring from space

Abstract Spectrally resolved thermal radiances measured from orbit with an accuracy in brightness temperature of 100 mK constitute a critical observation for climate monitoring. The design of a small, low-cost instrument capable of accuracies of better than 100 mK , demonstrated on-orbit, is presented and analyzed. It is shown that systematic and random errors inherent in observations from space can be reduced to levels commensurate with the instrumental accuracy of 100 mK . Monitoring spectrally resolved radiance, accurate to 100 mK , is feasible, and constitutes a versatile climate Benchmark observation that is needed in the national research strategy.

Climate robustly linked to African civil war

We previously documented a link between climate variation and historical civil wars in sub-Saharan Africa (1). Buhaug (2) disputes this link, generating a series of animated news reports. The relationship between climate and conflict is an important topic that deserves careful scientific scrutiny, but we believe Buhaugs approach is undermined by basic econometric mistakes, leading to what is currently an unhelpful debate. We briefly describe two main shortcomings in his analysis here, with a full analysis available as a working paper (3).

Stratospheric controlled perturbation experiment: a small-scale experiment to improve understanding of the risks of solar geoengineering

Although solar radiation management (SRM) through stratospheric aerosol methods has the potential to mitigate impacts of climate change, our current knowledge of stratospheric processes suggests that these methods may entail significant risks. In addition to the risks associated with current knowledge, the possibility of ‘unknown unknowns’ exists that could significantly alter the risk assessment relative to our current understanding. While laboratory experimentation can improve the current state of knowledge and atmospheric models can assess large-scale climate response, they cannot capture possible unknown chemistry or represent the full range of interactive atmospheric chemical physics. Small-scale, in situ experimentation under well-regulated circumstances can begin to remove some of these uncertainties. This experiment—provisionally titled the stratospheric controlled perturbation experiment—is under development and will only proceed with transparent and predominantly governmental funding and independent risk assessment. We describe the scientific and technical foundation for performing, under external oversight, small-scale experiments to quantify the risks posed by SRM to activation of halogen species and subsequent erosion of stratospheric ozone. The papers scope includes selection of the measurement platform, relevant aspects of stratospheric meteorology, operational considerations and instrument design and engineering.

Stratospheric solar geoengineering without ozone loss

Significance The combination of emissions cuts and solar geoengineering could reduce climate risks in ways that cannot be achieved by emissions cuts alone: It could keep Earth under the 1.5-degree mark agreed at Paris, and it might stop sea level rise this century. However, this promise comes with many risks. Injection of sulfuric acid into the stratosphere, for example, would damage the ozone layer. Injection of calcite (or limestone) particles rather than sulfuric acid could counter ozone loss by neutralizing acids resulting from anthropogenic emissions, acids that contribute to the chemical cycles that destroy stratospheric ozone. Calcite aerosol geoengineering may cool the planet while simultaneously repairing the ozone layer. Injecting sulfate aerosol into the stratosphere, the most frequently analyzed proposal for solar geoengineering, may reduce some climate risks, but it would also entail new risks, including ozone loss and heating of the lower tropical stratosphere, which, in turn, would increase water vapor concentration causing additional ozone loss and surface warming. We propose a method for stratospheric aerosol climate modification that uses a solid aerosol composed of alkaline metal salts that will convert hydrogen halides and nitric and sulfuric acids into stable salts to enable stratospheric geoengineering while reducing or reversing ozone depletion. Rather than minimizing reactive effects by reducing surface area using high refractive index materials, this method tailors the chemical reactivity. Specifically, we calculate that injection of calcite (CaCO3) aerosol particles might reduce net radiative forcing while simultaneously increasing column ozone toward its preanthropogenic baseline. A radiative forcing of −1 W⋅m−2, for example, might be achieved with a simultaneous 3.8% increase in column ozone using 2.1 Tg⋅y−1 of 275-nm radius calcite aerosol. Moreover, the radiative heating of the lower stratosphere would be roughly 10-fold less than if that same radiative forcing had been produced using sulfate aerosol. Although solar geoengineering cannot substitute for emissions cuts, it may supplement them by reducing some of the risks of climate change. Further research on this and similar methods could lead to reductions in risks and improved efficacy of solar geoengineering methods.

Improved aerosol radiative properties as a foundation for solar geoengineering risk assessment

Side effects resulting from the deliberate injection of sulfate aerosols intended to partially offset climate change have motivated the investigation of alternatives, including solid aerosol materials. Sulfate aerosols warm the tropical tropopause layer, increasing the flux of water vapor into the stratosphere, accelerating ozone loss, and increasing radiative forcing. The high refractive index of some solid materials may lead to reduction in these risks. We present a new analysis of the scattering efficiency and absorption of a range of candidate solid aerosols. We utilize a comprehensive radiative transfer model driven by updated, physically consistent estimates of optical properties. We compute the potential increase in stratospheric water vapor and associated longwave radiative forcing. We find that the stratospheric heating calculated in this analysis indicates some materials to be substantially riskier than previous work. We also find that there are Earth-abundant materials that may reduce some principal known risks relative to sulfate aerosols.

Reply to Sutton et al.: Relationship between temperature and conflict is robust

In a recent paper, we documented strong historical linkages between temperature and civil conflict in Africa (1). Sutton et al. (2) raise two concerns with our findings: that the relationship between temperature and war is based on common trends and is therefore spurious, and that our model appears overly sensitive to small specification changes. Both concerns reflect a basic misunderstanding of the analysis.

Stratospheric ozone over the United States in summer linked to observations of convection and temperature via chlorine and bromine catalysis

Significance Stratospheric ozone is one of the most delicate aspects of habitability on the planet. Removal of stratospheric ozone over the polar regions in winter/spring has established the vulnerability of ozone to halogen catalytic cycles. Elevated ClO concentrations engendered, in part, by heterogeneous catalytic conversion of inorganic chlorine to free radical form on ubiquitous sulfate−water aerosols, govern the rate of ozone removal. We report here observations of the frequency and depth of penetration of convectively injected water vapor into the stratosphere, triggered by severe storms that are specific to the central United States in summer, and model their effect on lower stratospheric ozone. This effect implies, with observed temperatures, increased risk of ozone loss over the Great Plains in summer. We present observations defining (i) the frequency and depth of convective penetration of water into the stratosphere over the United States in summer using the Next-Generation Radar system; (ii) the altitude-dependent distribution of inorganic chlorine established in the same coordinate system as the radar observations; (iii) the high resolution temperature structure in the stratosphere over the United States in summer that resolves spatial and structural variability, including the impact of gravity waves; and (iv) the resulting amplification in the catalytic loss rates of ozone for the dominant halogen, hydrogen, and nitrogen catalytic cycles. The weather radar observations of ∼2,000 storms, on average, each summer that reach the altitude of rapidly increasing available inorganic chlorine, coupled with observed temperatures, portend a risk of initiating rapid heterogeneous catalytic conversion of inorganic chlorine to free radical form on ubiquitous sulfate−water aerosols; this, in turn, engages the element of risk associated with ozone loss in the stratosphere over the central United States in summer based upon the same reaction network that reduces stratospheric ozone over the Arctic. The summertime development of the upper-level anticyclonic flow over the United States, driven by the North American Monsoon, provides a means of retaining convectively injected water, thereby extending the time for catalytic ozone loss over the Great Plains. Trusted decadal forecasts of UV dosage over the United States in summer require understanding the response of this dynamical and photochemical system to increased forcing of the climate by increasing levels of CO2 and CH4.

Airborne interferometer for atmospheric emission and solar absorption

The interferometer for emission and solar absorption (INTESA) is an infrared spectrometer designed to study radiative transfer in the troposphere and lower stratosphere from a NASA ER-2 aircraft. The Fourier-transform spectrometer (FTS) operates from 0.7 to 50 mum with a resolution of 0.7 cm(-1). The FTS observes atmospheric thermal emission from multiple angles above and below the aircraft. A heliostat permits measurement of solar absorption spectra. INTESAs calibration system includes three blackbodies to permit in-flight assessment of radiometric error. Results suggest that the in-flight radiometric accuracy is ~0.5 K in the mid-infrared.