Summary for policymakers Technical summary 1. The climate system - an overview 2. Observed climate variability and change 3. The carbon cycle and atmospheric CO2 4. Atmospheric chemistry and greenhouse gases 5. Aerosols, their direct and indirect effects 6. Radiative forcing of climate change 7. Physical climate processes and feedbacks 8. Model evaluation 9. Projections of future climate change 10. Regional climate simulation - evaluation and projections 11. Changes in sea level 12. Detection of climate change and attribution of causes 13. Climate scenario development 14. Advancing our understanding Glossary Index Appendix.

Climate change 2001: the scientific basis

The planetary boundaries framework defines a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system. Here, we revise and update the planetary boundary framework, with a focus on the underpinning biophysical science, based on targeted input from expert research communities and on more general scientific advances over the past 5 years. Several of the boundaries now have a two-tier approach, reflecting the importance of cross-scale interactions and the regional-level heterogeneity of the processes that underpin the boundaries. Two core boundaries—climate change and biosphere integrity—have been identified, each of which has the potential on its own to drive the Earth system into a new state should they be substantially and persistently transgressed.

/pdf/planetary-boundaries-guiding-human-development-on-a-changing-5gmf909etg.pdf

Planetary boundaries: Guiding human development on a changing planet

Increasing population and consumption are placing unprecedented demands on agriculture and natural resources. Today, approximately a billion people are chronically malnourished while our agricultural systems are concurrently degrading land, water, biodiversity and climate on a global scale. To meet the world's future food security and sustainability needs, food production must grow substantially while, at the same time, agriculture's environmental footprint must shrink dramatically. Here we analyse solutions to this dilemma, showing that tremendous progress could be made by halting agricultural expansion, closing 'yield gaps' on underperforming lands, increasing cropping efficiency, shifting diets and reducing waste. Together, these strategies could double food production while greatly reducing the environmental impacts of agriculture.

https://escholarship.org/content/qt6xw5g085/qt6xw5g085.pdf?t=ovfwpc

Solutions for a cultivated planet

Background:
VSEARCH is an open source and free of charge multithreaded 64-bit tool for processing and preparing metagenomics, genomics and population genomics nucleotide sequence data. It is designed as an alternative to the widely used USEARCH tool (Edgar, 2010) for which the source code is not publicly available, algorithm details are only rudimentarily described, and only a memory-confined 32-bit version is freely available for academic use.

Methods:
When searching nucleotide sequences, VSEARCH uses a fast heuristic based on words shared by the query and target sequences in order to quickly identify similar sequences, a similar strategy is probably used in USEARCH. VSEARCH then performs optimal global sequence alignment of the query against potential target sequences, using full dynamic programming instead of the seed-and-extend heuristic used by USEARCH. Pairwise alignments are computed in parallel using vectorisation and multiple threads.

Results:
VSEARCH includes most commands for analysing nucleotide sequences available in USEARCH version 7 and several of those available in USEARCH version 8, including searching (exact or based on global alignment), clustering by similarity (using length pre-sorting, abundance pre-sorting or a user-defined order), chimera detection (reference-based or de novo), dereplication (full length or prefix), pairwise alignment, reverse complementation, sorting, and subsampling. VSEARCH also includes commands for FASTQ file processing, i.e., format detection, filtering, read quality statistics, and merging of paired reads. Furthermore, VSEARCH extends functionality with several new commands and improvements, including shuffling, rereplication, masking of low-complexity sequences with the well-known DUST algorithm, a choice among different similarity definitions, and FASTQ file format conversion. VSEARCH is here shown to be more accurate than USEARCH when performing searching, clustering, chimera detection and subsampling, while on a par with USEARCH for paired-ends read merging. VSEARCH is slower than USEARCH when performing clustering and chimera detection, but significantly faster when performing paired-end reads merging and dereplication. VSEARCH is available at https://github.com/torognes/vsearch under either the BSD 2-clause license or the GNU General Public License version 3.0.

Discussion:
VSEARCH has been shown to be a fast, accurate and full-fledged alternative to USEARCH. A free and open-source versatile tool for sequence analysis is now available to the metagenomics community.

/pdf/vsearch-a-versatile-open-source-tool-for-metagenomics-3dmyvav0wl.pdf

VSEARCH: a versatile open source tool for metagenomics

Changes in Atmospheric Constituents and in Radiative Forcing

Long-term Aqua and Terra MODIS (MODerate resolution Imaging Spectroradiometer) Collections 5.1 and 6.1 (c051 and c061, respectively) aerosol data have been combined with AERONET (AERosol RObotic NETwork) ground-based sun photometer observations to examine trends in aerosol optical thickness (AOT, at 550 nm) over Northern Europe for the months April to September. For the 1927 and 1559 daily coincident measurements that were obtained for c051 and c061, respectively, MODIS AOT varied by 86 and 90%, respectively, within the predicted uncertainty of one standard deviation of the retrieval over land (ΔAOT = ±0.05 ± 0.15·AOT). For the coastal AERONET site Gustav Dalen Tower (GDT), Sweden, larger deviations were found for MODIS c051 and c061 (79% and 75%, respectively, within predicted uncertainty). The Baltic Sea provides substantially better statistical representation of AOT than the surrounding land areas and therefore favours the investigations of trends in AOT over the region. Negative trends of 1.5%...

Trends in MODIS and AERONET derived aerosol optical thickness over Northern Europe

The cloud nucleation scavenging process was studied during a joint campaign of the EUROTRAC sub-project Ground-based Cloud Experiment. It was found that the particle size has a strong influence on the partitioning of particles between the cloud droplet and the interstitial aerosol reservoirs. A new aerosol sampling unit, the relative humidity processing system, was employed for the extraction of particles with a low growth-ability with respect to increased relative humidity. The system supplied tracer elements on the particle growth-ability. These elements could be used to identify a factor related to particle hygroscopic properties, which was in effect as a selector of cloud condensation nuclei. DOI: 10.1034/j.1600-0889.1992.t01-1-00012.x

Elemental composition of fog interstitial particle size fractions and hydrophobic fractions related to fog droplet nucleation scavenging

Measurements of vertical profiles and level averages of ozone over the north central Atlantic near the Azores are presented. Lagrangian experiments were carried out in clean air and polluted air, and differences between the cases are discussed. Significant vertical structure was found in the profiles from both cases. Trajectory analysis indicates that the source regions for ozone in the marine boundary layer and in the air above the inversion capping the boundary layer were different. No significant production or destruction of ozone in the boundary layer was observed in the clean case. No substantial differences in ozone concentration between cloudy and clear air were observed, although cloud processes in the polluted case may have been partially responsible for an observed overall reduction in boundary layer ozone concentration.

Ozone in the marine atmosphere observed during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange

Regional aerosol properties from satellite observations: ACE-1, TARFOX and ACE-2 results

The radiative heating and cooling of the atmosphere is affected by perturbations of CO 2 , primary aerosols, and chemically-active greenhouse compounds (CH 4 , N 2 O, CFCs), and by secondary compounds (tropospheric ozone, sulfate, and organic aerosols) that are formed in the atmosphere through a variety of chemical and physical processes. While the concentrations of these secondary compounds are dominated by the surface emissions of their gas phase precursors, they are also closely coupled to meteorological parameters: temperature, wind, and the hydrological cycle (moisture, precipitation, and clouds), and to solar radiation (photo-dissociation). Therefore, climate changes due to global warming from anthropogenic greenhouse additions may perturb atmospheric concentrations of chemically-active climate compounds and thus the oxidation capacity of the atmosphere, providing feedback to the climate system. As the climatic states and surface precursor emissions exhibit distinctively different regional characteristics, these climate–chemistry interactions will play an important role in future climate changes that will disturb different areas differently.

Kevin J. Noone

Papers

Trends in MODIS and AERONET derived aerosol optical thickness over Northern Europe

Elemental composition of fog interstitial particle size fractions and hydrophobic fractions related to fog droplet nucleation scavenging

Ozone in the marine atmosphere observed during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange

Regional aerosol properties from satellite observations: ACE-1, TARFOX and ACE-2 results

Climate–Chemistry Interaction: Future Tropospheric Ozone and Aerosols