Oxygen-poor waters occupy large volumes of the intermediate-depth eastern tropical oceans. Oxygen-poor conditions have far-reaching impacts on ecosystems because important mobile microorganisms avoid or cannot survive in hypoxic zones. Climate models predict declines in oceanic dissolved oxygen produced by global warming. The researchers constructed a 50-year time series of dissolved-oxygen concentration for select tropical oceanic regions by augmenting a historical database with recent measurements.

A new paper shows that regional and even global temperatures are being temporarily held down by a natural jostling of the climate system, driven in large part by vacillating ocean currents.

The effects of global warming over the coming decades will be modified by shorter-term climate variability. Finding ways to incorporate these variations will give us a better grip on what kind of climate change to expect.

The Eocene

On geological timescales, carbon dioxide enters the atmosphere through volcanism and organic matter oxidation and is removed through mineral weathering and carbonate burial. An analysis of ice-core CO2 records and marine carbonate chemistry indicates a tight coupling between these processes during the past 610,000 years, which suggests that a weathering feedback driven by atmospheric CO2 leads to a mass balance between CO2 sources and sinks on long timescales.

The generally warm and ice-free conditions of the Eocene epoch rapidly declined to the cold and glaciated state of the Oligocene epoch. Geochemical evidence from deep-sea sediments resolves in detail the climatic events surrounding this transition.

In densely populated coastal areas, reactions of polluted air with sea salt aerosol from the ocean can lead to high surface ozone levels that affect air quality.

There may be more to global warming than we thought. On top of the effect of human-made carbon emissions, natural changes in the warm ocean currents travelling to the icy north may be helping to heat up the entire northern hemisphere.