Hunga Tonga-Hunga Ha’apai Volcano Impact Model Observation Comparison (HTHH-MOC) Project: Experiment Protocol and Model Descriptions

The 2022 Hunga volcanic eruption injected a significant amount of water vapor and a moderate amount of sulfur dioxide into the stratosphere causing observable responses in the climate system. We have developed a model-observation comparison project to investigate the evolution of volcanic water and aerosols, and their impacts on atmospheric dynamics, chemistry, and climate, using several state-of-the-art chemistry climate models. The project goals are: 1. Evaluate the current chemistry-climate models to quantify their performance in comparison to observations; and 2. Understand atmospheric responses in the Earth system after this exceptional event and investigate the potential impacts in the projected future. To achieve these goals, we designed specific experiments for direct comparisons to observations, for example from balloons and the Microwave Limb Sounder satellite instrument. Experiment 1 is a free-running ensemble experiment from 2022 to 2031. Experiment 2 is a nudged-run experiment from 2022 to 2023 using observed meteorology. To allow participation of more climate models with varying complexities of aerosol simulation, we include two sets of simulations in Experiment 2: Experiment 2a is designed for models with internally-generated aerosol while Experiment 2b is designed for models using prescribed aerosol surface area density. We take model results from the previously developed Tonga-MIP to fulfill Experiment 3, which focuses on the initial dispersion and microphysical evolution of aerosol and water plumes. Experiment 4 is designed to understand the climate impact on the mesosphere from 2022–2027, for which the experiment design is the same as Experiment 1 but for models that resolve the upper stratosphere and mesosphere

Indicators of Global Climate Change 2023: annual update of key indicators of the state of the climate system and human influence

Intergovernmental Panel on Climate Change (IPCC) assessments are the trusted source of scientific evidence for climate negotiations taking place under the United Nations Framework Convention on Climate Change (UNFCCC). Evidence-based decision-making needs to be informed by up-to-date and timely information on key indicators of the state of the climate system and of the human influence on the global climate system. However, successive IPCC reports are published at intervals of 5–10 years, creating potential for an information gap between report cycles. We follow methods as close as possible to those used in the IPCC Sixth Assessment Report (AR6) Working Group One (WGI) report. We compile monitoring datasets to produce estimates for key climate indicators related to forcing of the climate system: emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, the Earth's energy imbalance, surface temperature changes, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes. The purpose of this effort, grounded in an open-data, open-science approach, is to make annually updated reliable global climate indicators available in the public domain (https://doi.org/10.5281/zenodo.11388387, Smith et al., 2024a). As they are traceable to IPCC report methods, they can be trusted by all parties involved in UNFCCC negotiations and help convey wider understanding of the latest knowledge of the climate system and its direction of travel. The indicators show that, for the 2014–2023 decade average, observed warming was 1.19 [1.06 to 1.30] °C, of which 1.19 [1.0 to 1.4] °C was human-induced. For the single-year average, human-induced warming reached 1.31 [1.1 to 1.7] °C in 2023 relative to 1850–1900. The best estimate is below the 2023-observed warming record of 1.43 [1.32 to 1.53] °C, indicating a substantial contribution of internal variability in the 2023 record. Human-induced warming has been increasing at a rate that is unprecedented in the instrumental record, reaching 0.26 [0.2–0.4] °C per decade over 2014–2023. This high rate of warming is caused by a combination of net greenhouse gas emissions being at a persistent high of 53±5.4 Gt CO2e yr−1 over the last decade, as well as reductions in the strength of aerosol cooling. Despite this, there is evidence that the rate of increase in CO2 emissions over the last decade has slowed compared to the 2000s, and depending on societal choices, a continued series of these annual updates over the critical 2020s decade could track a change of direction for some of the indicators presented here.HORIZON EUROPE Framework ProgrammeH2020 European Research CouncilResearch Councils UKEngineering and Physical Sciences Research CouncilPeer Reviewe

F1850_2000_CALIPSO_NO_UT_5XBC

RFP runs output of CALIPSO corrected simulations (5XBC

E_1850_2000_CALIPSO_NO_UT_5XBC

CAM4 SOM simulation with CALIPSO corrected BC vertical distribution (5xBC)

F1850_no_aerosols

RFP runs no aerosol

E_1850_2000_CALIPSO_NO_UT_1XBC

Data from CAM4 coupled to SOM with prescribed CALIPSO corrected BC aerosols

F1850_2000_CALIPSO_NO_UT_10XBC

RFP runs output of CALIPSO corrected simulations (10XBC

E_1850_noaerosols

CAM4-SOM no aerosol ru

The Hunga Tonga-Hunga Ha'apai's volcanic plume properties as observed during the Brazil Volcano (BraVo) experiments

International audienceThe Hunga Tonga-Hunga Ha'apai (HTHH) eruption will remain an exceptional event, not by the amount of SO2 injected but by the unprecedented levels of H2O released into the atmosphere at altitudes never observed in the satellite era. Although HTHH injected only 0.42 Tg of SO2, the stratospheric aerosol optical depth persisted for at least 1.5 years at levels 3-4 times higher than what was expected based on equivalent injection by other tropical volcanoes. To shed light on this eruption, the Brazil Volcano (BraVo) experiment, which started in May 2022, deployed a suite of lightweight balloon-borne sensors to measure water vapor, ozone, and aerosol optical, microphysical, and chemical properties. During this presentation, we will address the following science questions: What are the optical, physical, and chemical properties of the HTHH plume observed during BraVo? Did HTHH inject a significant amount of sea salt into the stratosphere? What are the implications of HTHH eruption on radiation and climate? The balloon-borne measurements of the plume will be compared with satellite observations from CALIPSO and SAGE-III/ISS. In addition, the GEOS-Chem and ECHAM simulations will be used to assess the impacts of HTHH eruption on stratospheric aerosol optical depth, radiation, and climate