Abstract
The Arctic hydrological cycle has significant global implications, affecting deep ocean circulation through freshwater fluxes. However, attributing observed changes in the Arctic moisture budget remains challenging due to limited reliable observations. A recent study evaluated past changes in the hydrological cycle over the Arctic using CMIP6 historical simulations. The study compared simulations under various external forcings, including natural-plus-anthropogenic (ALL), greenhouse gas (GHG), natural (NAT), and aerosol (AER) forcings. Results indicated that Arctic precipitation and evaporation increased under ALL and GHG forcings but decreased under AER forcing. The study found that during summer, increased Arctic precipitation was mainly due to enhanced poleward moisture transport, while winter moistening was more influenced by increased surface evaporation over sea-ice retreat areas. In contrast, AER forcing led to decreased Arctic precipitation due to reduced evaporation over sea-ice advance areas during cold months.
Introduction
The Arctic climate system has experienced dramatic changes, including rapid warming and abrupt sea-ice melting, which can impact the Arctic hydrological cycle. Changes in Arctic precipitation can influence global climate by modulating the Atlantic meridional overturning circulation. The salinity distribution in the Arctic Ocean is affected by net precipitation, river discharge, sea ice formation, and ice melt. Positive freshwater fluxes into the Arctic could lower surface salinity and strengthen stratification, decreasing deep water formation.
Results
Changes in Arctic Moisture Budget
Long-term trends in precipitation, evaporation, and moisture transport to the Arctic were compared using CMIP6 models. ALL simulations showed a steady increase in precipitation and evaporation after an initial decrease in the 1960s. GHG simulations exhibited monotonic increases over the past 60 years, while AER simulations showed negative long-term trends due to decreases until the 1980s followed by stabilization. The influence of volcanic eruptions on the moisture budget was not evident.
Transport and Evaporation Contribution to Precipitation Change
The study quantified the relative contributions of surface evaporation and poleward moisture transport changes to Arctic precipitation trends. Enhanced surface evaporation during winter played a significant role in contributing to the increases in Arctic precipitation under ALL and GHG simulations.
Moisture Transport to the Arctic
The meridional moisture flux (MMF) across 70°N was analyzed, with contributions from mean meridional circulation (MMC), stationary eddies (SE), and transient eddies (TE). The study found that MMF is strongest in summer due to higher moisture levels, with GHG having a stronger MMF than other forcings.
Discussions
The study highlights the importance of understanding historical responses of Arctic hydrology to individual forcing for attributing observed changes. It demonstrates that both moisture transport and local evaporation contribute to atmospheric moisture and precipitation in the Arctic.
Methods
CMIP6 Simulation Data
Historical changes in the Arctic moisture budget were investigated using multi-model datasets from CMIP6 individual forcing experiments. The Arctic region was defined as 70°N–90°N.
Moisture Budget Analysis
The moisture budget of the Arctic atmosphere was analyzed by comparing contributions from poleward moisture transport and surface evaporation.
Vertically Integrated Meridional Moisture Flux
Poleward MMF across 70°N was calculated by integrating daily northward wind component and specific humidity through an atmospheric column.
Regional Contribution to MMF
The study separated MMF trends into contributions from the Pacific (90°E to 90°W) and Atlantic (90°W to 90°E) sectors.
Data Availability
CMIP6 data are available at https://esgf-node.llnl.gov/projects/cmip6/.
Code Availability
The source codes for this study are available from the authors upon reasonable request.
SDGs, Targets and Indicators
The article discusses issues related to the Arctic hydrological cycle, which has global implications through its impact on deep ocean circulation and freshwater fluxes. The Sustainable Development Goals (SDGs) that are addressed or connected to the issues highlighted in the article include:
- SDG 13: Climate Action
- SDG 14: Life Below Water
- SDG 15: Life on Land
Specific targets under these SDGs can be identified based on the article’s content:
- Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters.
- Target 14.3: Minimize and address the impacts of ocean acidification, including through enhanced scientific cooperation at all levels.
- Target 15.1: Ensure the conservation, restoration, and sustainable use of terrestrial and inland freshwater ecosystems and their services, in particular forests, wetlands, mountains, and drylands, in line with obligations under international agreements.
Indicators mentioned or implied in the article that can be used to measure progress towards the identified targets include:
- Indicator for Target 13.1: Changes in Arctic moisture budget components such as precipitation and evaporation.
- Indicator for Target 14.3: Changes in Arctic freshwater fluxes that affect ocean salinity and circulation patterns.
- Indicator for Target 15.1: Trends in sea-ice extent and retreat areas, which impact the Arctic hydrological cycle.
The provided explanations refer to specific information from the article to support the analysis of relevant SDGs, targets, and indicators.
| SDGs | Targets | Indicators |
|---|---|---|
| SDG 13: Climate Action | Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters. | Changes in Arctic moisture budget components such as precipitation and evaporation. |
| SDG 14: Life Below Water | Target 14.3: Minimize and address the impacts of ocean acidification, including through enhanced scientific cooperation at all levels. | Changes in Arctic freshwater fluxes that affect ocean salinity and circulation patterns. |
| SDG 15: Life on Land | Target 15.1: Ensure the conservation, restoration, and sustainable use of terrestrial and inland freshwater ecosystems and their services, in particular forests, wetlands, mountains, and drylands, in line with obligations under international agreements. | Trends in sea-ice extent and retreat areas, which impact the Arctic hydrological cycle. |
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Fuente: nature.com
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