Carbon Dioxide Removal (CDR) will be necessary to fulfil the hundreds of pledges to reach net-zero by 2050. As with any industry, standard methodologies and certification are crucial to guarantee successful and reliable activities. However, buyers and policymakers currently face challenges in evaluating the ecosystem of CDR certification. The issue is not with CDR, nor with individual certifications – some of which may be very robust – but with the lack of transparency in the overall ecosystem. To bring some clarity, we present a snapshot of the CDR certification and standards ecosystem for the year 2021–2022. We find a complex ecosystem with at least 30 standard developing organizations proposing at least 125 standard methodologies for carbon removal from 23 different CDR activities and selling 27 different versions of certification instruments in voluntary and compliance markets. This exercise reveals many more existing standards for nature-based than for engineering-based activities and more diversity from standards serving the voluntary rather than the compliance market. It also highlights a proliferation of standards for the same activity, and a plethora of activities without standards. The process revealed ambiguity on what constitutes carbon removal, with many standards certifying activities that remove CO₂ already in the environment as well as activities that avoid or reduce new emissions by sequestering the carbon into reservoirs. This mapping highlights key gaps and potential starting points for reforms to strengthen the CDR certification industry; it also underscores the need for independent oversight.

Millions of people in the arid Southwest United States rely on snow-fed Colorado River water. Dust deposition on snow accelerates snowmelt, posing a challenge for water managers who also need to grapple with increased likelihood of drought due to climate change. Dust production is thought to increase during drought, but the impact of drought on dust deposition is unclear. To answer this question, total dust mass accumulation rate (DMAR) reconstructions were developed from sediment cores from three lakes in the San Juan Mountains, Colorado, spanning the last ~15,000 years. Monte-Carlo end-member analysis of particle size and elemental composition, which incorporates measurement and model uncertainties, was combined with age uncertainty to estimate DMAR for each lake. We also synthesize the records providing the first Holocene DMAR reconstruction for the region. The records show little relation between periods of frequent and severe drought (e.g. during medieval megadroughts) and periods of higher DMAR, although there is considerable uncertainty at short timescales. We find instead that sediment availability, modulated by natural or human-mediated geomorphic processes that generate sediment, and transport mechanisms are the key drivers. DMAR was highest during the Late Glacial-Interglacial Transition (LGIT, 15–11 kyr BP) and in the last 250 years, periods when sediment availability was enhanced. DMAR increased by 60% (16–85% 75% highest density region range) compared with the late-Holocene baseline starting in the 1770s and peaking in the 1840s, associated with the intensification of human activities. Human-induced dustiness also represents the highest interval of dust deposition in the last 11,000 years. Our results demonstrate that although the Colorado Plateau is naturally prone to dustiness, drought is a secondary driver of dust accumulation in the mountains. This suggests that land-use management decisions aimed at reducing land disturbance can mitigate future dust accumulation, despite projected increases in regional aridity.

Holocene climate reconstructions are useful for understanding the diverse features and spatial heterogeneity of past and future climate change. Here we present a database of western North American Holocene paleoclimate records. The database gathers paleoclimate time series from 184 terrestrial and marine sites, including 381 individual proxy records. The records span at least 4000 of the last 12 000 years (median duration of 10 725 years) and have been screened for resolution, chronologic control, and climate sensitivity. Records were included that reflect temperature, hydroclimate, or circulation features. The database is shared in the machine readable Linked Paleo Data (LiPD) format and includes geochronologic data for generating site-level time-uncertain ensembles. This publicly accessible and curated collection of proxy paleoclimate records will have wide research applications, including, for example, investigations of the primary features of ocean–atmospheric circulation along the eastern margin of the North Pacific and the latitudinal response of climate to orbital changes. The database is available for download at https://doi.org/10.6084/m9.figshare.12863843.v1 (Routson and McKay, 2020).

Dust emissions from southwestern North America (Southwest) impact human health and water resources. Whereas a growing network of regional dust reconstructions characterizes the long‐term natural variability of dustiness in the Southwest, short‐term fluctuations remain unexplored. We present a 4.5‐millennia near‐annual record of dust mass accumulation rates from the southern Rocky Mountains, CO. Using microscanning X‐ray fluorescence and a geochemical end‐member mixing model, the record confirms dust increased with human disturbance beginning around 1880 CE, reversing a long‐term decreasing trend potentially related to changes in effective moisture, wind, and vegetation. However, increases in dust mass accumulation rates do not correspond to years or periods of drought, as characterized by tree rings. This result suggests sediment supply and transport mechanisms have a strong influence on dust deposition. The record shows the Southwest is naturally prone to dustiness; however, human disturbances have a large influence on dust emissions, which can be mitigated by changing land use.

The U.S. Southwest is naturally prone to dust and drought. With a high risk of unprecedented drought in the future due to climate change, changes in the dust cycle are expected. Whereas paleo records of dust deposition from the region suggest that past megadroughts did not coincide with elevated dust levels, modern studies indicate higher dust during drier conditions. To examine this disagreement, we compare regional paleo records to output from the Community Earth System Model Last Millennium Ensemble experiment. We investigate the role of hydroclimate on dust emissions in the model and analyze how modeled dust during megadroughts compares to all other years. We find that bare ground, as directly modulated by the density of vegetation cover and indirectly by hydroclimate, is the primary control on simulated dust emissions in the Southwest. Furthermore, we find slightly (but significantly) higher dust emission during megadroughts than during years without megadroughts in the model. Using a simple forward modeling approach to assess the impact of age uncertainty in the regional dust records, we find that age uncertainty can explain most of the paleo data/model disagreement. The remaining difference could be related to processes that are not included in the model that inhibit dust emissions during drought, including brown vegetation and soil crusts. Our results suggest the dust‐drought nexus is a continuum and that the impact of drought on dust cycling is subtle.

Life cycle analysis (LCA) is deeply embedded in carbon accounting. LCA is valuable for qualitatively understanding technologies’ environmental footprints. However, ambiguities and insatiable data requirements make it ill-suited for quantitative analysis. Fortunately, accounting without LCA is possible, for example, by demanding that for every ton of carbon coming out of the ground, another ton must be sequestered. This “Carbon Takeback Obligation” (CTBO) policy would eliminate the need for tracking carbon through supply chains. With all supply chains already carbon balanced, it is sufficient to quantify the amount of carbon sequestered without subtracting upstream emissions. Our modeling shows that once full carbon neutrality is demanded, market forces alone will eliminate counterproductive sequestration technologies, approaches that release more CO₂ than they store. Complications arise during the transition where some carbon extraction is not yet balanced out by sequestration, as under some policies, counterproductive technologies could be introduced solely to game the system. We explore the economics of four transition pathways: a simple CTBO, a CTBO combined with permits required for all unbalanced carbon, a CTBO combined with a futures market, and permit-future hybrid schemes. A simple CTBO that does not add an economic burden on unmitigated carbon would incentivize low-cost, counterproductive technologies. Contrastingly, a CTBO policy that includes permits and/or futures will render such technologies uneconomical at any point in the transition. A policy with controlled futures would allow for rapid permit phaseout. Hybrid systems could lessen the initiation shock and bridge the transition time when market demand exceeds sequestration capacity.