What is climate change detection and attribution?

The field known as climate change detection and attribution began in the 1990s when scientists demonstrated that the increase in global average temperature during the 20th century could not be explained without accounting for human emissions of heat-trapping gases. This process is often called “climate change fingerprinting,” or just “fingerprinting.” When studies identify the fingerprint of climate change, this means scientists have determined that human-caused global warming plays a role in whatever trend or event is under investigation

Definitions

• Climate change fingerprinting studies positively identify, through detection or attribution analysis, the influence of human-caused global warming on observed trends or events.
• Detection and attribution studies demonstrate that the climate or a system affected by climate has changed, and this change cannot be explained by internal variability alone (Hegerl et al., 2010). For example, early studies detected observed warming during the 20th century that could not be explained in the absence of human-caused climate change.
• Attribution studies identify the factors affecting a detected climate change and evaluate the relative contributions of these factors. For example, Hegerl et al. (2007) attribute about a third of the warming in the first half of the twentieth century to human caused greenhouse gas emissions.

What is the state of climate detection and attribution science?

The fingerprint of global warming has been firmly established for many trends and events. At a more fundamental level, global warming has changed the background conditions in which all climate-related events occur. In this sense climate change is now affecting all weather events and, by pushing systems beyond their thresholds, climate change can be responsible for a disproportionate amount of an event's impact.

In the US, detection and attribution studies have identified the fingerprint of climate change in rising and extreme temperatures, coastal flooding, extreme precipitation events, reduced snowpack and hydrological changes in the West, increased average precipitation in the Northeast and North Central US, increased drought risk, extreme hurricane seasons in the central Pacific, changing atmospheric patterns, and heightened wildfire risk.

Globally, studies have shown climate change is directly implicated in long-term warming of the atmosphere and ocean, record-breaking and extreme heat events, changes in average precipitation and atmospheric moisture content, extreme precipitation, sea level rise, extreme Arctic warmth and sea ice loss, tropical cyclone activity, ocean chemistry, biological systems, and large scale circulation.

Where can I find studies that find climate change fingerprints?

Much of the work of detecting the influence of climate change and attributing it to specific impacts is summarized in major climate assessments including the Intergovernmental Panel on Climate Change Assessment Reports (IPCC ARs) and the United States National Climate Assessments (US NCAs). The American Meteorological Society also publishes an annual report of studies assessing how human-caused climate change may have affected the strength and likelihood of individual extreme events from the previous year.

The science is advancing quickly, however, and major climate assessments only come out every few years. To bridge the gap, Climate Signals tracks detection and attribution studies in real time.

What about studies that don't find climate change fingerprints?

When a study finds no link to climate change, it does not necessarily follow there is no connection—it only indicates that particular direction of research was unable to find evidence indicating a link. The 2016 National Academy of Sciences report on extreme weather and climate change states that the failure to find the fingerprint of climate change “should not be regarded as evidence…of…no effect.” And further that it does not “necessarily mean that the effect is small.” According to the Academy report, the blanket statement that we cannot attribute any single event to climate change “is no longer true.”

More broadly, the Academy reports that: “all events occur in a climate system that has been changed by human influences,” and that “it is impossible to rule out some contribution from climate change to any extreme event.” In the climate system “everything is connected.”