Comment on cp-2022-69

<strong class="journal-contentHeaderColor">Abstract.</strong> Volcanic eruptions are the dominant cause of natural variability in climate forcing on timescales up to multidecadal. Large volcanic eruptions lead to global-scale climate effects and influence the carbon cycle on long timescales. However, estimating the frequency of eruptions is challenging. Here we assess the frequency at which eruptions with particular deposition fluxes are observed in the EPICA Dome C ice core over the last 200 kyr. Using S isotope analysis we confirm that most of the largest peaks recorded at Dome C are from stratospheric eruptions. The cumulative frequency through 200 kyr is close to linear, suggesting an approximately constant rate of eruptions. There is no evidence for an increase in the rate of events recorded in Antarctica at either of the last two deglaciations. Millennial variability is at the level expected from recording small numbers of eruptions, while multimillennial variability may be partly due to changes in transport efficiency through the Brewer–Dobson circulation. Our record of events with sulfate deposition rates <span class="inline-formula">&gt;</span> 20 and <span class="inline-formula">&gt;50</span> mg m<span class="inline-formula">^−2</span> contains 678 and 75 eruptions, respectively, over the last 200 kyr. Calibration with data on historic eruptions and analysis of a global Quaternary dataset of terrestrial eruptions indicates that sulfate peaks with deposition rates <span class="inline-formula">&gt;</span> 20 and <span class="inline-formula">&gt;50</span> mg m<span class="inline-formula">^−2</span> correspond to explosive eruptions of magnitude <span class="inline-formula">≥</span> 6.5 and <span class="inline-formula">≥7</span>, respectively. The largest recorded eruption deposited just over 300 mg m<span class="inline-formula">^−2</span>.

Abstract. In this study we report on new non-sea salt calcium (nssCa2+, mineral dust proxy) and sea salt sodium (ssNa+, sea ice proxy) records along the East Antarctic Talos Dome deep ice core in centennial resolution reaching back 150 thousand years (ka) before present. During glacial conditions nssCa2+ fluxes in Talos Dome are strongly related to temperature as has been observed before in other deep Antarctic ice core records, and has been associated with synchronous changes in the main source region (southern South America) during climate variations in the last glacial. However, during warmer climate conditions Talos Dome mineral dust input is clearly elevated compared to other records mainly due to the contribution of additional local dust sources in the Ross Sea area. Based on a simple transport model, we compare nssCa2+ fluxes of different East Antarctic ice cores. From this multi-site comparison we conclude that changes in transport efficiency or atmospheric lifetime of dust particles do have a minor effect compared to source strength changes on the large-scale concentration changes observed in Antarctic ice cores during climate variations of the past 150 ka. Our transport model applied on ice core data is further validated by climate model data. The availability of multiple East Antarctic nssCa2+ records also allows for a revision of a former estimate on the atmospheric CO2 sensitivity to reduced dust induced iron fertilisation in the Southern Ocean during the transition from the Last Glacial Maximum to the Holocene (T1). While a former estimate based on the EPICA Dome C (EDC) record only suggested 20 ppm, we find that reduced dust induced iron fertilisation in the Southern Ocean may be responsible for up to 40 ppm of the total atmospheric CO2 increase during T1. During the last interglacial, ssNa+ levels of EDC and EPICA Dronning Maud Land (EDML) are only half of the Holocene levels, in line with higher temperatures during that period, indicating much reduced sea ice extent in the Atlantic as well as the Indian Ocean sector of the Southern Ocean. In contrast, Holocene ssNa+ flux in Talos Dome is about the same as during the last interglacial, indicating that there was similar ice cover present in the Ross Sea area during MIS 5.5 as during the Holocene.

SummaryBackgroundAedes aegypti spread pathogens affecting humans, including dengue, Zika, and yellow fever viruses. Anthropogenic climate change is altering the spatial distribution of Ae aegypti and therefore the locations at risk of vector-borne disease. In addition to climate change, natural climate variability, resulting from internal atmospheric processes and interactions between climate system components (eg, atmosphere–land and atmosphere–ocean interactions), determines climate outcomes. However, the role of natural climate variability in modifying the effects of anthropogenic climate change on future environmental suitability for Ae aegypti has not been assessed fully. In this study, we aim to assess uncertainty arising from natural climate variability in projections of Ae aegypti suitability up to the year 2100.MethodsIn this mathematical modelling study, we developed an ecological model in which Ae aegypti population dynamics depend on climate variables (temperature and rainfall). We used 100 projections of future climate from the Community Earth System Model, a comprehensive climate model that simulates natural climate variability as well as anthropogenic climate change, in combination with our ecological model to generate a range of equally plausible scenarios describing the global distribution of suitable conditions for Ae aegypti up to 2100. Each of these scenarios corresponds to a single climate projection, allowing us to explore the difference in Ae aegypti suitability between the most-suitable and the least-suitable projections.FindingsOur key finding was that natural climate variability generates substantial variation in future projections of environmental suitability for Ae aegypti. Even for projections generated under the same Shared Socioeconomic Pathway (SSP) scenario (SSP3–7.0), in 2100 climatic conditions in London might be suitable for Ae aegypti for 0–5 months of the year, depending on natural climate variability.InterpretationNatural climate variability affects environmental suitability for important disease vectors. Some regions could experience vector-borne disease outbreaks earlier than expected under climate change alone.FundingEngineering and Physical Sciences Research Council and Wellcome Trust.

Prognoses regarding future climate scenarios hinge on the predictive skills of climate models. They must produce reliable estimates of the future mean climate state as well as future climate variability about the mean, resulting from the interference between natural climate variability and anthropogenic perturbations of the climate system. Natural climate variability originates from interactions between components of the climate systems and from perturbations external to the climate system. To validate model-generated climate variability against the whole range of natural variability, it is necessary to gather information on the temporal progression of Holocene climate variability. Distinct spatial climate regimes (climate-variability patterns) can be extracted from climate observations and facilitate the comparison between paleoclimate reconstructions and model results. Examples of instrumental observations and proxy data demonstrate the potential of such records to trace climate regimes through time. The dominant mode of today’s climate variability in Europe — the North Atlantic Oscillation — constitutes a climate regime, that can serve to provide an expectation in assessing Holocene climate variability. First attempts to reconstruct the history of the North Atlantic Oscillation during the last 300 years or so are summarized. Volcanic eruptions and solar variability constitute important external perturbations of the climate system that account for a significant portion of natural variability.

Missouri River streamflow increased substantially during the 20th century, with multiple large floods occurring since 1990. Using land surface models and water budget simulations, we examined the extent to which increased flow was driven by natural climate variability, anthropogenic climate trends, land‐use and land‐cover change (LULCC), and ecological effects of elevated atmospheric CO2. Natural climate variability (arising largely from coupled ocean‐atmosphere circulation systems in both the Pacific and North Atlantic) accounted for ∼765 m3 s−1 of the ∼900 m3 s−1 increase in flow since mid‐century, while anthropogenic climate trends negatively forced flow by increasing evapotranspiration more than precipitation. LULCC and elevated CO2 further increased simulated mean streamflow by ∼550 and ∼70 m3 s−1, respectively, relative to pre‐Industrial conditions and ∼100 and ∼65 m3 s−1 relative to mid‐20th century conditions. The LULCC effect was especially large in wet years, implying that current land cover is ill‐suited for buffering against extreme precipitation, likely in large part due to replacement of forest by cropland in the lower basin. Because increases in Missouri River flow over the past century were driven mostly by a recent (and likely transient) pluvial, our results suggest that flow in the basin could revert to a drier mean state when that pluvial ends, likely made worse by increased evaporative demand from anthropogenic warming.

The study aimed to calculate the livelihood vulnerability of organic and non-organic rice farmers' households to climate change. The sample was determined by a census comprising 60 organic and 80 non-organic rice farmers who lived in Pematang Sawa Sub-district, Tanggamus Region, Lampung Province, Indonesia. The livelihood vulnerability index (LVI) was measured based on seven main indicators: natural disaster and climate variability, agriculture profile, food security, water security, food/rice consumption, educational attainment, and income. The results showed that organic rice farmers' households were more vulnerable in terms of natural disaster and climate variability, water security, food consumption, education, and income, while non-organic rice farmers' households were more vulnerable in terms of agriculture profile and food security. Using the LVI framework approach of the Intergovernmental Panel on Climate Change (LVI-IPCC), non-organic rice farmers’ households were found to be more vulnerable to climate change than organic rice farmers' households. To better observe the vulnerability of organic and non-organic rice farmers' households to climate change, future studies should be conducted in two distant locations (e.g., different regions or provinces) because different climate components could significantly influence the findings. Rice farmers' households could become less vulnerable by providing them with objective climate information that will encourage them to adopt the necessary climate change adaptation and mitigation strategies. Further support is needed in the form of resources aid programs, such as the provision of irrigation systems or pumping wells, as well as livestock aid to increase the farmers’ income.

Climate change will impact both mean and extreme precipitation, having potentially significant consequences on water resources. The implementation of efficient adaptation measures must rely on the development of reliable projections of future precipitation and on the assessment of their related uncertainty. Natural climate variability is a key uncertainty component, which can result in apparent decadal trends that may be greater or lower than the long-term underlying anthropogenic climate change trend. The goal of the present study is to assess how natural climate variability affects the ability to detect the climate change signal for mean and extreme precipitation. Annual and seasonal total precipitation are used as indicators of the mean, whereas annual and seasonal maximum daily precipitation are used as indicators of extremes. This is done using the CanESM2 50-member and CESM1 40-member large ensembles of simulations over the 1950–2100 period. At the local scale, results indicate that natural climate variability will dominate the uncertainty for annual and seasonal extreme precipitation going up to the end of the century in many parts of the world. The climate change signal can, however, be reliably detected much earlier at the regional scale for extreme precipitation. In the case of annual and seasonal total precipitation, the climate change signal can be reliably detected at the local scale without resorting to a regional analysis. Nonetheless, natural climate variability can impede the detection of the anthropogenic climate change signal until the middle to late century in many parts of the world for mean and extreme precipitation.

Effect of climate variability on estimation of greenhouse parameters: Usefulness of a pre-instrumental temperature record

The increased trends of extreme precipitation events over China have been partially attributed to global warming, while it is unclear how the natural climate variability affect these variations in extreme rainfall trends. Here we examine the contributions of large‐scale modes climate variability from the Pacific Ocean, which are represented by El Niño‐Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), on the trends of seasonal extreme events across China. Results show that the effects of climate variability modes on precipitation extremes exhibit evidently spatiotemporal characteristics at the seasonal scale. A significant positive trend is found over southeastern and northwestern China in four seasons, and substantial increases in two types of extreme events are also seen over northwestern China in spring and winter. Most of the seasonal trends of extreme precipitation events can be explained by the trends of the principal components. El Niño (La Niña) and PDO–like sea surface temperature (SST) anomalies over the Pacific have a close linkage with the variations in precipitation extremes. By modulating the large‐scale atmospheric circulations, these Pacific SST anomalies associated with climatic oscillations, such as ENSO and PDO, provide the conducive conditions responsible for the occurrences of seasonal precipitation extremes across China. The seasonal trends of extreme events can be largely explained by the variability of the ENSO and PDO episodes, with a relatively larger modulation of PDO as compared to ENSO. These researches have important implications for improving seasonal flood disaster predictability and climate model performances.

Drylands contain a third of the organic carbon stored in global soils; however, the long-term dynamics of soil organic carbon in drylands remain poorly understood relative to dynamics of the vegetation carbon pool. We examined long-term patterns in soil organic matter (SOM) against both climate and prescribed fire in a Chihuahuan Desert grassland in central New Mexico, USA. SOM concentration was estimated by loss-on-ignition from soils at 0–20 cm depth each spring and fall for 25 years (1989–2014) in unburned desert grassland and from 2003 to 2014 following a prescribed fire. SOM concentration did not have a long-term trend but fluctuated seasonally at both burned and unburned sites, ranging from a minimum of 0.9% to a maximum of 3.3%. SOM concentration declined nonlinearly in wet seasons and peaked in dry seasons. These long-term results contrast not only with the positive relationships between aboveground net primary production and precipitation for this region, but also with previous reports that wetter sites have more SOM across drylands globally, suggesting that space is not a good substitute for time in predicting dryland SOM dynamics. We suggest that declines in SOM in wet periods are caused by increased soil respiration, runoff, leaching, and/or soil erosion. In addition to tracking natural variability in climate, SOM concentration also decreased 14% following prescribed fire, a response that magnified over time and has persisted for nearly a decade due to the slow recovery of primary production. Our results document the surprisingly dynamic nature of soil organic matter and its high sensitivity to climate and fire in a dry grassland ecosystem characteristic of the southwestern USA.

The Sudd in South Sudan, formed by the White Nile’s Baḥr al-Jabal section, is one of the largest and most important wetlands in the world. Communities in the region almost exclusively depend on fisheries for food and livelihoods. Although threatened by over-exploitation and habitat changes, fish populations are also affected by climate change. Using semi-structured questionnaires, we assessed fisherfolk’s opinions of how recent variation in climate affected their livelihoods and the environment. Fisherfolk perceived that climate had changed in the past decade and were negatively impacted by this. Interviewees reported average higher temperatures, a greater frequency of floods and droughts, unpredictable timing of seasons, and erratic rainfall. Destruction of fishing villages/camps, loss and damage of fishing equipment, shifts in the fishing calendar, reduction of fish trade, and fish catch declines as well as psycho-social problems were given as the major consequences of climate change. Causes of climate change and variability were perceived to be linked to uncontrolled harvest of forest resources, anger of God and ancestors, and natural variability in climate. Most respondents expressed a desire to adopt more responsible behavior such as planting trees and establishing community nurseries, being educated on climate change risks, and sustainable fisheries management. Our results show that fisherfolk in the Sudd are troubled by climate change impacts on their livelihoods and on fish populations. In South Sudan, climate change has been reported from hydroclimatological data but concrete impacts on people remain largely unknown and of little concern because of recent wars and the poor economy. Our study provides an example of how fisherfolks’ local ecological knowledge (LEK) can be used as an early warning system of the negative impacts on livelihoods and fish populations and support adaptation to the changing climate.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10113-022-01928-w.

A comprehensive review of Holocene paleoenvironmental data has been prepared, providing the basis for evaluating natural variability in climate and ecosystem dynamics in the northern Columbia River basin. The paleoenvironmental record reveals four major climatic shifts and a number of less well-defined climatic changes throughout the Holocene. The major climate changes are (1) a cool or cold, late-glacial climate at the end of the last glaciation (&gt;11 500 cal. year BP), (2) an interval of drought and maximum summer warmth during the early Holocene (ca. 10500 to 8000 cal. year BP), (3) a mid-Holocene trend towards a cooler, more moist climate (ca. 8000 to ca. 4000 cal. year BP), and (4) a relatively stable climate persisting from ca. 4000 cal. year BP until the arrival of European settlers. Air temperatures have warmed by about 1 °C over the past century. Minor climate events that are emerging as global in nature include Little Ice Age (1200–150 BP) conditions, and a late Holocene cool wet period (3500–2500 BP). These are observed in some study sites examined in this paper and may be related to large-scale cycles of 2800–2000 and 1500 years. A discussion of changing atmospheric circulation patterns, and the causes of long-term climatic change are included, together with a discussion of the implications of the paleoenvironmental record for understanding future climate, and the likely response of communities and ecosystems.

&amp;lt;p&amp;gt;MIS 4, a key paleoclimatic interval for the last glacial inception, is characterized by a rapid CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; drop of approx. ~28ppm and a large drop in temperature (as seen in Antarctic ice cores). SSTs in the North Atlantic are thought to be coupled to AMOC strength, whereby various proxies suggest a weaker and shoaled AMOC during the transition from MIS5a to MIS4. Furthermore, several millennial events also occurred during MIS 4, including Heinrich Stadial 6 and DO events 16-19. MIS 4 is thus an ideal interval to study and eventually to disentangle, glacial-interglacial and millennial variability.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Here, we present high resolution planktonic and benthic foraminifera geochemical data from several marine sediment cores from the Iberian Margin (including stable isotope and trace element data). The Iberian Margin is a prime location to study millennial-scale climate variability as isotope records of planktonic and benthic foraminifera simultaneously recorded rapid climate change expressed in Greenland and Antarctic ice cores, respectively, during the last glacial period. However, our results so far, suggest that surface ocean response at this site does not track Greenland temperature, as would be expected for this region of the North Atlantic. Perhaps the most striking, our planktic Mg/Ca record shows a late onset of rapid MIS 4 cooling at the start of Heinrich 6, and no clear millennial variability signal. This is in agreement with SST reconstructed using alkenones (Pailler and Bard, 2002) and planktonic foraminifera faunal assemblages (Salgueiro et al., 2010) from nearby core sites. Local d18O seawater reconstructions imply major hydrological changes in the region, which is supported by the &amp;amp;#8220;dry event&amp;amp;#8221; seen in speleothems from North Eastern Iberia (Perez-Mehias et al., 2019) and Italy (Columbu et al., 2020), just before Heinrich 6. We propose that the observed changes may reflect changes in regional ocean and atmospheric circulation patterns such as the interaction of the strength and position of the Azores Current, Iberian Poleward Current and the Subtropical Gyre, which in turn could depend on the larger scale AMOC and wind driven surface ocean changes due to glacial-interglacial and millennial variability. Further links to moisture transport, ice sheet growth and carbon cycle are yet to be investigated.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;strong&amp;gt;References&amp;lt;/strong&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Columbu, A., Chiarini, V., Sp&amp;amp;#246;tl, C., Benazzi, S., Hellstrom, J., Cheng, H. and De Waele, J., 2020. Speleothem record attests to stable environmental conditions during Neanderthal&amp;amp;#8211;modern human turnover in southern Italy.&amp;amp;#160;Nature Ecology &amp;amp; Evolution, 4(9), pp.1188-1195.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Pailler, D. and Bard, E., 2002. High frequency palaeoceanographic changes during the past 140&amp;amp;#8200;000 yr recorded by the organic matter in sediments of the Iberian Margin.&amp;amp;#160;Palaeogeography, Palaeoclimatology, Palaeoecology, 181(4), pp.431-452.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;P&amp;amp;#233;rez-Mej&amp;amp;#237;as, C., Moreno, A., Sancho, C., Mart&amp;amp;#237;n-Garc&amp;amp;#237;a, R., Sp&amp;amp;#246;tl, C., Cacho, I., Cheng, H. and Edwards, R., 2019. Orbital-to-millennial scale climate variability during Marine Isotope Stages 5 to 3 in northeast Iberia.&amp;amp;#160;Quaternary Science Reviews, 224, p.105946.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Salgueiro, E., Voelker, A., de Abreu, L., Abrantes, F., Meggers, H. and Wefer, G., 2010. Temperature and productivity changes off the western Iberian margin during the last 150&amp;amp;#160;ky.&amp;amp;#160;Quaternary Science Reviews, 29(5-6), pp.680-695.&amp;lt;/p&amp;gt;

Summertime ozone pollution has become increasingly severe over many parts of China in recent years. Due to lack of historical ozone observations, few studies have analyzed the linkage between natural climate variability and ozone levels for a long time series. This study uses the simulation datasets from CMIP6 to explore the effects of El Niño-Southern Oscillation (ENSO) on summertime (June/July/August) surface ozone concentrations in central-eastern China (CEC; 20°N-42°N, 100°E-123°E) during the period of 1950-2014. Our results show that, after excluding the emission-related trend, the detrended summertime daily mean surface ozone concentrations averaged over CEC in El Niño years (30.69ppb) are higher than those in La Niña events (29.34ppb). Compared to the summertime mean ozone of 1950-2014 (30.25ppb), the maximum anomalies in CMIP6 are 2.88ppb (9.52% higher) and - 5.52ppb (18.25% lower) in El Niño and La Niña years, respectively. In addition, the summertime MDA8 ozone of CEC is significantly correlated with the central-eastern equatorial Pacific SST (5°N-5°S, 170°W-120°W) (R = 0.29, P-value = 0.02). Such ozone increases/declines in El Niño/La Niña years are also found in satellite observations of OMI ozone. The results show that the ENSO affects the large-scale circulations over central-eastern China, which regulate the regional atmospheric stability and meteorological conditions (including horizontal wind fields, geopotential height, vertical velocity, surface air temperature, and precipitation) to influence the efficiency of ozone photochemical formation and transport. Our study makes better estimation and attribution of future surface ozone pollution in China.

The twentieth-century Northern Hemisphere surface climate exhibits a long-term warming trend largely caused by anthropogenic forcing, with natural decadal climate variability superimposed on it. This study addresses the possible origin and strength of internal decadal climate variability in the Northern Hemisphere during the recent decades. The authors present results from a set of climate model simulations that suggest natural internal multidecadal climate variability in the North Atlantic–Arctic sector could have considerably contributed to the Northern Hemisphere surface warming since 1980. Although covering only a few percent of the earth’s surface, the Arctic may have provided the largest share in this. It is hypothesized that a stronger meridional overturning circulation in the Atlantic and the associated increase in northward heat transport enhanced the heat loss from the ocean to the atmosphere in the North Atlantic region and especially in the North Atlantic portion of the Arctic because of anomalously strong sea ice melt. The model results stress the potential importance of natural internal multidecadal variability originating in the North Atlantic–Arctic sector in generating interdecadal climate changes, not only on a regional scale, but also possibly on a hemispheric and even a global scale.