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.

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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

Publisher Summary The chapter discusses the size distribution and chemical composition of cloud droplet residual particles in marine stratocumulus clouds observed during the mast experiment. Measurements of cloud droplet residual particle microphysics and chemistry were made in marine stratocumulus clouds off the central California coast during the Monterey area ship tracks (MAST) experiment in June, 1994. Typically, 80% or more of the residual particles were below 0.1 μm radius. While the mode size of residual particles was slightly higher in polluted clouds than in clean ones, the droplet population in the two cases was determined by the submicrometer aerosol. One explanation for the shift towards larger sizes in the residual particle size distributions for polluted versus clean clouds is a reduction of the peak supersaturation in the polluted clouds because of an increase in the rate at which water vapor is taken up by the larger number of particles present in the polluted clouds. Single particle analysis for samples taken in a clean marine boundary layer showed the residual particles larger than 0.1 μm radius to have been composed of sea salt and a combination of sea salt and sulfate. This composition is typical of the background marine boundary layer aerosol. Residual particles containing exclusively organic material, and also organic material plus CI were observed in a sample from a moderately polluted cloud. These clusters accounted for 182 of the 500 particles analyzed, indicating that organic particles were a substantial fraction of the cloud condensation nuclei in these particular clouds.

The size distribution and chemical composition of cloud droplet residual particles in marine stratocumulus clouds observed during the mast experiment

The Eagle UAV, built by IAI and marketed in Europe by EADS, can be considered a mature UAV. It is approximately 17 m in wingspan, weighs 1100 kg and can fl y up to 10 000 m altitude. The max speed is around 200 km/h and it has 24 hour endurance. The aircraft has a large cargo-bay in the middle of the fuselage around CG, which makes it easy to use payloads of different kinds as the different payload weight does not affect the CG. In other UAVs lighter payloads might have to be balanced with extra weights. The available volume is around 1 cubic metre and maximum payload weight around 250 kg. In the future, hardpoints will also be installed on the wings. These will be able to hold 50 kg each, making it possible to hang science pods on the vehicle.

/pdf/uavs-for-atmospheric-research-in-the-north-of-sweden-nhiu46tbu4.pdf

UAVs for atmospheric research in the north of Sweden

The North Atlantic Regional Aaosol Characterization Experiment (ACE-2) of the International Global Atmospheric Chemistry Project (IGAC) ran from 16 June to 25 July 1997. The results presented in this study are part of the "Clear-sky column closure experiment" (CLEARCOLUMN) activity, one of 6 ACE-2 activities. Clear-sky column closure experiments call for characterization of aerosol layers by simultaneous measurements using different techniques that can be related using models. A wide range of aerosol types was encountered throughout the ACE-2 area, including background Atlantic marine, European pollution-derived and African mineral dust. In a series of papers, we reported on ACE-2 CLEARCOLUMN results obtained by combining airborne sunphotometer and in-situ measurements taken aboard the Pelican aircraft, spaceborne NOAA/AVHRR data and ground-based lidar and sunphotometer measurements. Those and other CLEARCOLUMN results have been summarized previously. In this paper we only report on results not shown in this form.

/pdf/airborne-sunphotometer-airborne-in-situ-space-borne-and-2jouf5rz94.pdf

Airborne sunphotometer, airborne in-situ, space-borne, and ground-based measurements of tropospheric aerosol in ACE-2

Aerosol optical thickness (AOT) has decreased substantially in Europe in the summer half year (April–September) since 1980, with almost a 50% reduction in Central and Eastern Europe, according to Modern‐Era Retrospective analysis for Research and Applications, Version 2 (MERRA‐2) reanalysis. At the same time, strong positive trends in ERA5 reanalysis surface solar radiation downward for all‐sky and clear‐sky conditions (SSRD and SSRDc, respectively) and temperature at 2 m are found for Europe in summer during the period 1979–2020. The GEBA observations show as well strong increases in SSRD during the latest four decades. Estimations of changes in SSRDc, using the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model, show similarly strong increases when fed by MERRA‐2 AOT. The estimates of warming in this study, caused by increases in SSRD and SSRDc, are based on energy budget approximations and the Stefan Boltzmann law. The increases in near surface temperature, estimated both for clear‐sky and all‐sky conditions, are up to about 1°C for Central and Eastern Europe. The total warming over large parts of this region for clear‐sky conditions is however nearly double the global mean temperature increase of 1.1°C, while somewhat less for all‐sky conditions. The effects of aerosols on warming over the southerly Iberian Peninsula are weaker compared to countries further north. The rapid total warming over the Iberian Peninsula is probably caused by greenhouse warming, drier surface conditions, and to some degree decline in aerosols. Reduced cloud cover is found for large parts of Europe in summer during the latest four decades.

Unmasking the Effects of Aerosols on Greenhouse Warming Over Europe

In this chapter, we outline the causes of sea-level rise: thermal expansion, melting of glaciers and ice sheets, changes in land storage, and other residual sources. We describe observations of sea-level rise from a number of independent measurements such as tide gauges and satellites. These measurements show that sea level is rising (250 mm since 1850), and that sea-level rise is accelerating. We summarize current projections of sea-level rise, which range between 0.2 and 1.9 m by the end of the century, with most projections since 2007 being in the range of 1 m by 2100. We also discuss the impacts of sea-level rise on coastal communities and small island states.

Kevin J. Noone

Papers

The size distribution and chemical composition of cloud droplet residual particles in marine stratocumulus clouds observed during the mast experiment

UAVs for atmospheric research in the north of Sweden

Airborne sunphotometer, airborne in-situ, space-borne, and ground-based measurements of tropospheric aerosol in ACE-2

Unmasking the Effects of Aerosols on Greenhouse Warming Over Europe

Sea-Level Rise