Climate Science

Reputable Sources

Not all sources of information are created equal. Go to scientific organizations for your science–not to entertainment media, popular news, blogs, radio, or op-ed articles. Every scientific organization in the world has come to the same general conclusions about human-caused climate change: the Earth is warming, it's us, we're sure enough to act, and it's urgent.

There is scientific consensus about this understanding: http://climate.nasa.gov/scientific-consensus.

There is a big difference between scientific consensus and political consensus. It takes a consensus of all the available evidence to reach scientific consensus.

The Fourth National Climate Assessment (v1): Causes

This report summarizes what NASA, NOAA, the EPA, DOD, DOE, and other major US scientific organizations understand about climate change and how confident they are in that understanding based on all the available evidence.

From the two-page Executive Summary Highlights:

"This assessment concludes, based on extensive evidence, that it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century. For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence."

The term "extremely likely" indicates a 95-100% level of confidence.

The Fourth National Climate Assessment (v2): Impacts and Risks

The Overview provides a national summary and Chapter 18 is about impacts on the Northeast: https://nca2018.globalchange.gov/. From the Overview:

  • "Climate change creates new risks and exacerbates existing vulnerabilities in communities across the United States, presenting growing challenges to human health and safety, quality of life, and the rate of economic growth."

  • "Climate change affects the natural, built, and social systems we rely on individually and through their connections to one another. These interconnected systems are increasingly vulnerable to cascading impacts that are often difficult to predict, threatening essential services within and beyond the Nation’s borders."

  • "While mitigation and adaptation efforts have expanded substantially in the last four years, they do not yet approach the scale considered necessary to avoid substantial damages to the economy, environment, and human health over the coming decades."

  • "The seasonality of the Northeast is central to the region’s sense of place and is an important driver of rural economies. Less distinct seasons with milder winter and earlier spring conditions are already altering ecosystems and environments in ways that adversely impact tourism, farming, and forestry."

  • "The Northeast’s coast and ocean support commerce, tourism, and recreation that are important to the region’s economy and way of life. Warmer ocean temperatures, sea level rise, and ocean acidification threaten these services."

  • "Changing climate threatens the health and well-being of people in the Northeast through more extreme weather, warmer temperatures, degradation of air and water quality, and sea level rise. These environmental changes are expected to lead to health-related impacts and costs, including additional deaths, emergency room visits and hospitalizations, and a lower quality of life."

What's the rush?

At the current rate of GHG emissions from human activities, we only have several years before we will exceed the carbon budget that offers a 50:50 chance of holding global warming to 1.5˚C this century. The IPCC's Special Report on 1.5˚C of Global Warming shows potential emissions reduction paths we could follow to hold warming to 1.5˚C (pages 6 and 13): net-zero emissions by 2050 and negative emissions for the second half of the century to achieve an atmospheric CO2 concentration of 350 ppm or less before 2100.

This report also compares the differences in risks, impacts, and damages of global warming by 1.5˚C and by 2˚C. NASA summarized these differences in a summary report. The differences make it clear we share a responsibility to avoid 2˚C of warming.

The UN's Emissions Gap Report demonstrates the greatly increased difficulty of holding warming below 1.5˚ C if we delay for even just five more years.

Are we sure it's us?

Yes, we are sure. The climate has always changed, and we know why through science. The IPCC's Fifth Assessment Report (Chapter 8) reviews all the natural and man-made climate forces since 1750 (warming and cooling). The two main warming forces are the man-made increase in CO2 (gray) and CH4 (methane, the main contributor in the well-mixed greenhouse gases represented in light green) in Figure 8.18 (page 699).

The IPCC Sixth Assessment Report: IPCC AR6 WG1.

  • "It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred."

  • "Observed warming is driven by emissions from human activities, with

greenhouse gas warming partly masked by aerosol cooling."

The Carbon Cycle: short- versus long-term carbon (ie. biomass versus fossil fuels)

Why is burning wood different than burning coal? Because when a tree falls, all or most of all of the carbon in it will end up back in the air in the span of a human life-time and another tree can grow in it's place, removing the same amount of carbon from the air in that same timeframe. It's a balanced, sustainable cycle (land-use changes not withstanding).

Fossil fuels consist of carbon that hasn't been in the air for hundreds of millions of years, and when it was in the air, the climate was something for which dinosaurs, not humans, were well adapted. Our infrastructure, food and water systems, bodies, and nature around us are not suited to withstand the higher global temperatures of that previous age.

Pick an ecosystem, any ecosystem

Ecosystems around the world are already being impacted by human-caused climate change, from coral reefs to Arctic tundra. This is a major driver of the Earth's sixth mass extinction.

For example, we've lost 50% of the world's tropical coral reefs in the last 30 years from 1˚C of global warming since 1900. Most of that warming occurred in the last four decades.

The differences in damage to life on Earth between 1.5˚C and 2˚C of global warming are enormous. According to the IPCC SR15 report (above), we'll lose 70-90% of the world's coral reefs from 1.5˚C warming and 98-100% from 2˚C warming. The difference is about 20 years of emissions at the current rate.

1.5˚C of warming is virtually impossible to avoid, but our energy policy choices over the next decade will determine our future emissions and our future temperatures.

See also: The Sixth Extinction by Elizabeth Kolbert.

A YouTube playlist of science, economics, policy, and climate communication videos

The Earth's climate is changing, and we know why through science with a high level of confidence. The political climate must change so we can address the causes. There are bipartisan ways to make that happen that will also help make our Democracy stronger: YouTube PlayList.

Why CFD 2020