The consensus that humans are causing recent global warming is shared by 90%-100% of publishing climate scientists according to six independent studies by co-authors of this paper. Those results are consistent with the 97% consensus reported by Cook et al (Environ. Res. Lett. 8 024024) based on 11 944 abstracts of research papers, of which 4014 took a position on the cause of recent global warming. A survey of authors of those papers (N=2412 papers) also supported a 97% consensus. Tol (2016 Environ. Res. Lett. 11 048001) comes to a different conclusion using results from surveys of nonexperts such as economic geologists and a self-selected group of those who reject the consensus. We demonstrate that this outcome is not unexpected because the level of consensus correlates with expertise in climate science. At one point, Tol also reduces the apparent consensus by assuming that abstracts that do not explicitly state the cause of global warming ('no position') represent nonendorsement, an approach that if applied elsewhere would reject consensus on well-established theories such as plate tectonics. We examine the available studies and conclude that the finding of 97% consensus in published climate research is robust and consistent with other surveys of climate scientists and peer-reviewed studies.

New particle formation in the atmosphere is an important parameter in governing the radiative forcing of atmospheric aerosols. However, detailed nucleation mechanisms remain ambiguous, as laboratory data have so far not been successful in explaining atmospheric nucleation. We investigated the formation of new particles in a smog chamber simulating the photochemical formation of H 2 SO 4 and organic condensable species. Nucleation occurs at H 2 SO 4 concentrations similar to those found in the ambient atmosphere during nucleation events. The measured particle formation rates are proportional to the product of the concentrations of H 2 SO 4 and an organic molecule. This suggests that only one H 2 SO 4 molecule and one organic molecule are involved in the rate-limiting step of the observed nucleation process. Parameterizing this process in a global aerosol model results in substantially better agreement with ambient observations compared to control runs.aerosol particles | atmospheric nucleation | new particle formation | sulfuric acid A tmospheric aerosols affect the radiative balance in the Earth's atmosphere and influence cloud formation, thereby playing a central role in climate forcing. They also have an important impact on visibility and human health. Many of these effects depend on the particle size distribution, which is governed by the emission of primary particles on the one hand and formation of new particles on the other hand. New particle formation events have been observed frequently and worldwide, in boreal forests, coastal, rural, and urban regions, as well as the free troposphere (1). Their contribution to the regional and global budget of atmospheric particles is likely to be significant though it is still poorly constrained (2-5). A detailed understanding of atmospheric nucleation processes is therefore needed.Observations in the planetary boundary layer revealed a consistent correlation between sulfuric acid (H 2 SO 4 ) and the concentration of newly formed particles (6-9), where the particle formation rate can be described with a simple power law:The exponent m was found to consistently vary between 1 and 2. According to the nucleation theorem (10), this suggests that the critical cluster (the smallest stable "particle") contains only one or two H 2 SO 4 or sulfuric acid-containing molecules. Classical binary (H 2 SO 4 -water) and ternary (H 2 SO 4 -NH 3 -water) mechanisms predict much higher values of the exponent and fail to explain the ambient observations (11, 12). Therefore, new approaches such as H 2 SO 4 cluster activation (13) (for m ¼ 1) and kinetic nucleation (14) (for m ¼ 2) have been developed trying to explain the observed new particle formation events. Recently the formation of organosulfate clusters was suggested to explain the chemistry behind the cluster activation or kinetic mechanisms and thus atmospheric nucleation (15). From detailed analyses of nucleation and growth it was inferred that sesquiterpenes might be involved in new particle formation. On the other hand, a number...

[1] Compounds assigned to be oxidation products of isoprene (2-methyl-1,3-butadiene) have recently been observed in ambient aerosols, suggesting that isoprene might play an important role in secondary organic aerosol (SOA) formation due to its large global source strength. SOA yields from photooxidation of isoprene and NO x in a chamber agree fairly well with previous data. Matrix assisted laser desorption/ionization mass spectrometry showed the formation of high molecular weight compounds over the course of 15-hour experiments. Concurrently, the volatility of the SOA decreased markedly as observed by a tandem differential mobility analyzer. The volume fraction remaining of SOA at 150°C increased steadily from 5 to 25% during the same experiments. These observations are attributed to oligomerization reactions occurring in the aerosol phase. Under dry conditions a lower volatility was observed. Citation: Dommen, J

A ground-based sampling system named Ice-CVI is introduced that is able to extract small ice particles with sizes between 5 and 20 μm out of mixed-phase clouds. The instrument is based on a counterflow virtual impactor (CVI) removing interstitial particles and is supplemented by additional modules that pre-segregate other constituents of mixed-phase clouds. Ice particles of 20 μm and smaller are expected to grow only by water vapor diffusion and there is a negligible probability that they scavenge aerosol particles by impaction and riming. Thus, their residuals which are released by the Ice-CVI can be interpreted as the original ice nuclei (IN). In a first field test within the Cloud and Aerosol Characterization Experiment (CLACE-3) at the high alpine research station Jungfraujoch, the collection behavior of the single components and the complete system was evaluated under atmospheric sampling conditions. By comparing parameters measured by the Ice-CVI with corresponding results obtained from other inlets or with in-situ instrumentation it is verified that the small ice particles are representatively collected whereas all other mixed phase cloud constituents are effectively suppressed. In a case study it is observed that supermicrometer particles preferentially serve as IN although in absolute terms the IN concentration is dominated by sub-micrometer particles. Mineral dust (Si), non-volatile organic matter and black carbon could be identified as IN components by means of different chemical analyses. The latter suggests an anthropogenic influence on the heterogeneous ice nucleation in supercooled, tropospheric clouds.