The case for climate action is having a hard time in Washington these days. While public officials acknowledge the climate is changing, they’re not necessarily saying why or what should be done about it.
Let’s clear up a few points.
1.The Earth is heating up.
Scientists have measured global temperatures for over a hundred years and see that the Earth is getting hotter. The trend can be best visualized by comparing each year’s average temperature with the long-term average. This figure shows observations of the world’s annual average temperature made by the National Oceanic and Atmospheric Administration (NOAA). It compares each year’s temperature to the average over the entire century. Blue bars are years that were cooler than average and red bars are years that were warmer than average. In recent decades, the years have always been hotter. If there were no long-term temperature trend, you would expect a mix of red and blue bars throughout the record. That’s not what we see.
Source: The National Oceanic and Atmospheric Administration (NOAA)
2. Human activity is largely responsible for this warming.
Over geologic time, the Earth’s average temperature has changed as a result of the sun’s output, the tilt and position of the Earth in its orbit, and the concentration of greenhouse gases. Scientists have developed a good understanding of the natural variations in these factors by examining different proxies for ancient temperatures. Observations tell us that these natural factors have not been changing over the last hundred years or so in a way that would explain the observed temperature increases.
In contrast, greenhouse gases have been changing in a way that can explain the observed temperature increases. The pre-eminent record of modern atmospheric carbon dioxide (CO2) concentrations is based at the Scripps Institute of Oceanography. Researchers there have been sampling pristine air from a mountaintop in Hawaii every month since 1958 and analyzing its composition. Their observations show that both the concentration and isotopic composition of CO2 is changing, and is consistent with manmade sources, including the carbon emissions from burning fossil fuels.
Moreover, physics tells us how different climate variables will change the temperature of the atmosphere at different heights. For example, changes in solar output will heat the atmosphere uniformly, while changes due to greenhouse gases will warm the surface but cool the higher part of the atmosphere (the stratosphere).
The National Centers for Environmental Information, run by NOAA, conduct monthly observations of atmospheric temperatures at different levels. Its 39-year record shows that the temperature change is not uniform. This is consistent with the effect of greenhouse gases, and inconsistent with other types of natural effects (e.g., changes in the sun’s output).
3. The impacts of climate change are growing, and we need to stop adding to the problem.
The result of this buildup of greenhouse gases is that we’re trapping heat within the climate system. The basic physics behind this has been establish for over 100 years. But climate change isn’t just a matter of the air temperature being a few degrees warmer.
- Higher levels of CO2 in the atmosphere lead to increased acidity in the oceans, which is damaging to shellfish and other marine life.
- Warmer water temperatures and melting of glaciers (due to warmer air temperatures) increase average sea level across the globe.
- Climate change is affecting the frequency and intensity of heat waves, heavy rainfall events, and several other types of extreme weather and disasters.
Some observed climate changes are not bad. For example, growing seasons are lengthening in some parts of the country and costs for winter heating go down when temperatures are mild. But the overall impacts are estimated to be negative and costly.
The good news is that we’re making progress, and that we have many of the tools right now to make a difference, including expanding use of renewable power; zero-carbon nuclear power, carbon capture, use and storage; energy efficiency technologies, and electric vehicles. Many businesses, cities, and states are pursuing clean energy and clean transportation to improve public health, save money, and create jobs.
The question is not whether climate change is happening, but what we want to do about it.
The Center for Climate and Energy Solutions and The Climate Registry co-convene the Climate Leadership Conference each year around the prestigious Climate Leadership Awards. The CLC is dedicated to professionals addressing global climate change through policy, innovation, and business solutions.
Climate Leadership Conference
March 1-3, 2017 at the Marriott Downtown Chicago
C2ES will host or co-host the following events at the 2017 Climate Leadership Conference.
March 1, 2017
9 a.m. -- 11 a.m.
How Cities Are Driving a New Climate Future
Hosted by: C2ES and the Great Lakes and St. Lawrence Cities Initiative
This event highlights two important aspects of local climate action: 1) how cities and their leaders are using their platform to facilitate transformative climate solutions, and 2) how cities and private actors are implementing local solutions. Speakers will engage attendees in a discussion about how cities are driving the new climate future through political leadership and action, and present tangible ideas that attendees can take home and put into practice. Who should attend? Local leaders, practitioners and private sector partners.
March 1, 2017
11 a.m. -- 12:30 p.m.
What Makes Infrastructure Resilient?
Hosted by: C2ES
What makes infrastructure resilient? Cities and businesses across the country are taking action to strengthen the resilience of their buildings, transportation systems, energy and water services, and telecommunication systems to climate change. This session will explore issues associated with resilient infrastructure, including challenges and barriers, priorities, innovative solutions, and opportunities for collaboration. Facilitated discussions will allow participants to discuss some of these issues based on their own experiences, and exchange ideas about infrastructure needs and opportunities.
January 26, 2017
Contact Laura Rehrmann, firstname.lastname@example.org
C2ES again ranks among top environmental think tanks
WASHINGTON -- The Center for Climate and Energy Solutions (C2ES) is honored to be recognized once again as one of the world’s leading environmental think tanks.
C2ES ranked fourth among environment policy think tanks in the University of Pennsylvania’s 2016 Global Go To Think Tank Index, based on a worldwide survey of more than 2,500 scholars, academics, public and private donors, policymakers, and journalists.
C2ES was also recently named the top U.S. energy and environment think tank by Prospect magazine for helping lay the groundwork for the Paris Agreement.
“C2ES’s consistently high ranking is a tribute to our unique ability to bring together diverse stakeholders to achieve practical, commonsense solutions,” said C2ES President Bob Perciasepe. “We work with companies, cities, states, and national governments to develop and implement economically sound, innovative policies to reduce greenhouse gas emissions, promote clean energy, and strengthen resilience to climate impacts.”
“I congratulate and thank our outstanding staffers, supporters, partners, and board members, including Board Chairman Ted Roosevelt IV, who have helped C2ES achieve and maintain our success,” Perciasepe said.
This is the 10th year for the University of Pennsylvania’s Think Tanks and Civil Societies Program to rank the world’s 6,846 leading think tanks. According to the report, the top environmental think tanks “excel in research, analysis and public engagement on a wide range of policy issues with the aim of advancing debate, facilitating cooperation between relevant actors, maintaining public support and funding, and improving the overall quality of life.”
About C2ES: The Center for Climate and Energy Solutions (C2ES) is an independent, nonpartisan, nonprofit organization working to forge practical solutions to climate change. Our mission is to advance strong policy and action to reduce greenhouse gas emissions, promote clean energy, and strengthen resilience to climate impacts. Learn more at www.c2es.org.
The Montreal Protocol on Substances that Deplete the Ozone Layer is considered the world’s most successful international environmental treaty.
Under the Protocol, nations phased out chlorofluorocarbons (CFCs) – a class of compounds that were used mostly in aerosol sprays, refrigerants, foams and as solvents, and were damaging the protective ozone layer that shields the planet from harmful ultraviolet radiation. Recent evidence shows that the ozone hole over Antarctica is beginning to repair itself because of efforts under the Protocol to reduce ozone-depleting substances.
Because ozone-depleting substances and many of their substitutes are also potent greenhouse gases, their phase-out under the Montreal Protocol is critical to international efforts to address climate change.
Following nearly a decade of talks, a landmark agreement was reached October 15, 2016, at the 28th Meeting of the Parties of the Montreal Protocol in Kigali, Rwanda, to phase down hydrofluorocarbons (HFCs), CFC substitutes that, while not harmful to the ozone layer, are a fast-growing source of potent greenhouse gases contributing to climate change.
HFCs are widely used in refrigeration and air conditioning, foam blowing, and other applications. Though they now account for less than 1 percent of global greenhouse gas emissions, HFCs are extremely potent greenhouse gases whose use is projected to grow rapidly, particularly in developing countries.
The Kigali Amendment sets out a schedule of targets and timetables for all developed and developing countries to phase down their use of HFCs. The amendment links these control requirements with a renewed commitment by developed countries to provide financial support for developing countries through the Protocol’s Multilateral Fund. The agreement sets out key principles for how the fund will transition from supporting projects aimed at safeguarding the ozone layer to spurring action focused on climate protection.
Because HFCs have a relatively short atmospheric lifetime (compared to carbon dioxide), their phasedown could reduce temperature changes in 2100 by an estimated 0.5 degrees Celsius. These reductions are critical to meeting the long-term goal of the Paris Agreement to keep warming well below 2 degrees.
The Montreal Protocol is a part of the 1985 Vienna Convention for the Protection of the Ozone Layer, which commits its 197 parties to protect human health and environment against “adverse effects” of human-induced changes to the ozone layer.
The Montreal Protocol, which was adopted in 1987 and entered into force in 1989, limits the consumption and production of ozone-depleting substances. Since its entry into force, the Montreal Protocol has phased out over 98 percent of the world’s consumption of ozone-depleting substances.
- Blog: Nations agree on historic HFC phasedown
- Bob Perciasepe's statement
- Not-in-Kind Alternatives to High Global Warming HFCs (2016)
- Status of Legal Challenges: Patents Related to the Use of HFO1234YF in Auto Air Conditioning (2016)
- Ten Myths About Intellectual Property Rights and the Montreal Protocol (2016)
- Approaches to Structuring a High Ambient Temperature Exemption (2016)
- Technological Change in the Production Sector under the Montreal Protocol (2015)
- Patents and the Role of the Multilateral Fund (2015)
- Addressing Short-Lived Climate Pollutants
International negotiators are gathering in Kigali, Rwanda, with the goal of phasing down one of the most potent and rapidly expanding greenhouse gases affecting the climate.
Momentum is building for taking action on hydrofluorocarbons (HFCs), a family of industrial chemicals used worldwide in air conditioners, refrigeration, foam products, and aerosols.
- On the sidelines of the recent U.N. General Assembly, more than 100 nations signed a declaration calling for an amendment to the Montreal Protocol to ambitiously deal with HFCs, with an early freeze date for developing countries and an early first reduction step for developed countries.
- To jump start the transition away from HFCs, 16 donor nations have offered $27 million in new and additional money for use by developing countries in limiting HFC use in 2017. Donor countries are also committing to support the longer-term phase-down costs under the Montreal Protocol’s Multilateral Fund.
- In an unprecedented move, a group of philanthropists (19 foundations and private individuals including Bill Gates and Tom Steyer) have offered an additional $53 million to developing countries to support efforts to move from HFCs to more energy-efficient alternatives.
- More than 500 companies and organizations issued a call to action in support of an ambitious agreement on an HFC phasedown at the 28th Meeting of the Parties to the Montreal Protocol October 10-14.
Action on HFCs is the single most significant step nations can take this year to advance the goal established in the Paris Agreement of limiting global temperature increases to well below 2 degrees Celsius. Estimates are that an ambitious HFC amendment would reduce global warming by as much as 0.5 degrees by the end of the century.
While momentum for an ambitious agreement this year is strong and building, it is by no means assured. Even with more than 100 nations on board, reaching an international consensus in Kigali will not be easy.
A large number of developed and developing countries have supported a developing country freeze in HFC use beginning around 2021, but India has supported a 2030 freeze date and Gulf Cooperation Council countries proposed a 2028 freeze.
Issues under discussion include the costs and availability of alternatives, the role and timing of patent protections, the rules governing support of projects under the Multilateral Fund, and the need for updated standards for the safe handling and use of more flammable refrigerant alternatives. While there is general support for incorporating enhanced energy efficiency into the transition away from HFCs, there are questions about the ways to achieve this objective.
Solutions are on the table for all of these issues. Given progress to date and the financial resources now available to developing countries to support an ambitious HFC amendment, agreement in Kigali is well within reach. The costs of acting to reduce HFCs are small compared to the very real and present costs of inaction to limit changes to our climate.
- Two feet of rain – that is about four months’ worth – fell in parts of Louisiana over the past few days, forcing thousands to flee their homes as water rose to the rooftops. More than a dozen people have died in the flooding.
- On July 30, nearly six inches of rain fell in two hours in Ellicott City, Md., turning Main Street into a raging river that swept away cars, tore up storefronts, and killed two people.
- About a month earlier, up to 10 inches of rain fell in 12 hours in parts of West Virginia, causing flooding that killed 26.
Heavy downpours are expected to become more frequent in a warming world. That’s because warmer air can hold more water vapor. For each degree of warming, the air’s capacity to hold water vapor goes up by about 7 percent. An atmosphere with more moisture can produce more intense precipitation, which is what we’ve been seeing.
Last year, flash and river floods killed 176 people in the United States, more than for any other weather-related disaster.
Better infrastructure -- both “green,” like using soil and vegetation to absorb rainfall, and “gray,” using manmade materials for pipes and walls -- can give the water someplace to go other than into homes and businesses.
In urban areas, where concrete and asphalt have replaced water-absorbing soils, rain gardens and porous pavements can reduce the amount of storm water pouring through the streets, or overwhelming water treatment plants.
In other areas, more extensive storm protection infrastructure, like flood walls and storm water storage and pumping facilities, may be needed. Nashville is considering building a $110 million flood wall and pumping system after flooding in May 2010 killed 11 and caused more than $2 billion in private property damage. After initially blocking the plan, the council this summer authorized completing designs and seeking community input.
Flood protection is costly, but so is flood cleanup. The National Oceanic and Atmospheric Administration estimates four severe floods – in Texas and Oklahoma in May 2015, South Carolina in October 2015, Texas and Louisiana in March 2016, and Houston in April 2016 – caused an estimated $7 billion in damages and killed 69 people.
More frequent and intense downpours are one of the impacts we can expect from climate change. Cities, states and businesses will need to work together to strengthen infrastructure and protect properties and lives.
|Innovation to Power the Nation (and the World): Reinventing our Climate Future event held at the Carnegie Institute of Science Auditorium. Keynote remarks by Michelle Lee, Under Secretary of Commerce for Intellectual Property and Director of the United States Patent and Trademark Office; and panelists including: Dr. Jayant Baliga, Dr. Kristina Johnson, Nathan Hurst, Bob Perciasepe and moderated by Amy Harder.|
Energy, business and policy experts agree: Current technologies aren’t enough to keep the world from warming more than 2 degrees Celsius by 2100, the ambitious goal of the Paris Agreement. We will need innovation to fill the gap.
Where do we need breakthroughs? What do we need do more, do differently or do faster to evolve our energy system to be efficient, dependable and low-carbon? What policies would help drive the innovation we need?
These are some of the questions that guided a recent discussion C2ES helped organize at the Carnegie Institution for Science.
U.S. Patent and Trademark Office Director Michelle K. Lee opened the conversation by emphasizing the importance of innovation to face the challenges posed by climate change. “History has shown us there are few challenges that innovative minds cannot overcome,” she said.
Here are some of the highlights of the discussion, which you can watch here:
We can vastly improve energy efficiency
Dr. B. Jayant Baliga, an inventor with 120 patents and a professor at North Carolina State University, sees an enormous opportunity to improve energy efficiency, not necessarily through new inventions, but by more widely using some of the technologies we already have.
One of Baliga’s inventions, the insulated gate bipolar transistor (IGBT), dramatically improves efficiency in power flow in everything from appliances to cars to factories, saving an estimated 100 trillion pounds of carbon dioxide emissions.
Using variable speed motor drives that take advantage of IGBTs can improve efficiency by 40 percent, but only about half of U.S. motors run on these drives, compared with nearly 100 percent in Europe, Baliga said. With two thirds of U.S. electricity used to run motors, the energy savings could be enormous.
Lighting consumes about a fifth of electricity in the U.S. Going from incandescent bulbs to CFLs reduces energy use 75 percent. But in the U.S., only 2 billion out of the 5 billion light sockets have CFL bulbs in them, Baliga said. “We need some encouragement for people to use these kinds of lights,” he said.
Business plays a crucial role
Businesses understand the importance of climate change for both their operations and customers. Nate Hurst, Chief Sustainability & Social Impact Officer at HP, said companies should examine their operations and supply chains to drive energy efficiency, and also make products that are as energy efficient as possible.
HP, along other multinational companies, recently pledged to power global operations with 100 percent renewable energy, with the goal of 40 percent by 2020. The company also announced a new commitment to achieve zero deforestation also by 2020, which means all HP paper and paper-based packaging will be derived from certified recycled sources.
Companies need to diversify their energy sources, but the biggest challenge is price. Hurst suggested government incentives and tax credits can play a role in bringing alternative energy prices down.
Policy is needed at the federal, state and city level
C2ES President Bob Perciasepe said policies to recognize the costs of greenhouse gas emissions, such as a price on carbon, can stimulate innovation. Cities, states and businesses are pressing forward with policies and actions to save energy and expand clean energy. C2ES recently launched an alliance with the U.S. Conference of the Mayors to bring businesses and cities together to speed deployment of new technologies.
One area where more innovation is needed is carbon capture, use and storage. “We know how to do it, but we have to find cheaper ways to do it,” Perciasepe said. “And we have to find ways to use carbon, not just shove it all back into the earth.” For example, the Ford company is testing ways to capture carbon emissions from its manufacturing plants to make plastic for use in the interior of cars.
Hydropower can play a key role
Dr. Kristina Johnson, an electrical engineer and former Undersecretary for Energy at the Department of Energy, said it’s crucial to find new ways to use renewable energy. Her company, Cube Hydro Partners, acquires and modernizes hydroelectric facilities and develops power at unpowered dams.
“When we built our first little power plant in an existing dam, it cost less than $20 million, but it was the equivalent of having planted a million fully grown trees in the rainforest, which would have been a billion dollars,” she said. Hydropower can help provide constant energy to fill in for wind and solar power, she said.
Other areas where innovation would boost clean energy would be small modular nuclear reactors, although more work needs to be done on handling the waste, and an economic way to store or reuse emissions from fossil fuel plants, she said.
The last question asked by moderator Amy Harder of The Wall Street Journal was: What is the most important invention society needs to make and bring to scale to address the challenge of climate change?
What our panelists said:
- A visionary new source of power,
- Enhanced versions of the sources already known, such as ocean currents or solar power,
- The right economic incentives to scale the solutions we already have, and
- New materials that can be reused and recycled without compromising quality.
Climate change is causing longer and hotter heat waves that take a toll on public health and on a community’s economy, prompting some local governments to take action.
Heat can be deadly. From 2006-2010, exposure to extreme heat resulted in 3,332 U.S. deaths. The elderly and the poor are among the most vulnerable due to pre-existing health issues and limited access to air conditioning. But young outdoor enthusiasts are also at risk. Five hikers died during a heat wave this summer in Arizona, where it got as hot as 120 degrees F.
Heat waves are not only dangerous, they’re also expensive. Extreme heat can damage crops and livestock, reduce worker productivity, drive up energy costs, and increase demand for water resources. A 2011 heat wave and associated drought in the Southwest and Southern Plains cost $12.7 billion.
A hotter, drier Southwest
While it’s hard to determine how climate change influences individual extreme weather events, we do know climate change exacerbates both their frequency and intensity.
In the Southwest, residents are expected to see an additional 13 to 28 extremely hot days (temperatures of 95F or hotter) by mid-century, and 33 to 70 additional days by the end of the century. Higher temperatures will also exacerbate droughts and fire cycles.
How to prepare
The Southwest region has already taken steps to prepare for the impacts of more extreme heat. This is especially critical for urban areas, where stretches of heat-absorbing concrete and asphalt create a heat island effect, increasing temperatures in some cities by up to 15 degrees above surrounding areas
In Southern California, the city government in Chula Vista is working to implement 11 strategies to help adapt to the impacts of climate change. They include using reflective or “cool” paving and roofing to reduce the urban heat island effect, and amending building codes to incentivize water reuse and lower demand for imported water.
In Arizona, the city of Phoenix’s Water Resource Plan includes short- and long-term strategies to deal with water shortage scenarios, including monitoring supplies and managing demand, developing increased well capacities for water storage, and coordinating with neighboring counties to secure additional water resources.
A council of local governments in Central New Mexico is working to determine the impacts of heat waves on infrastructure, including the role of extreme heat in degrading asphalt and pavement, and what types of pavement materials are most resilient to extreme heat.
Early efforts to improve climate resilience can help a community prepare for costly extreme weather events and more quickly bounce back from them. Local governments like the cities of Phoenix and Chula Vista and those in New Mexico are demonstrating strong leadership that can be an example for others. Coordinating with partners in state government and the business community, including through the C2ES Solutions Forum, can ensure local governments’ resilience plans provide maximum protection against the heat waves of the future.
Webinar: Financing Climate Resilience – What Are Our Options?
Extreme weather events and disasters are already damaging assets, disrupting supply chains, reducing productivity and revenues, and destroying livelihoods. Projected climate impacts will also likely hit the creditworthiness of companies, posing risks to financial institutions and may affect companies' credit ratings. The need to update infrastructure provides an opportunity to build in climate resilience.
This webinar explores options for financing resilience and features an interactive discussion with experts in the field about opportunities and potential challenges.
July 21, 2016
Noon – 1:30 p.m. ET
Managing Director for HUD Programs (Office of Recovery), New Jersey Energy Resilience Bank
Founder & CEO, re:focus partners
Science Fellow and Resilience Project Coordinator, Center for Climate and Energy Solutions
Fatima Maria Ahmad
Solutions Fellow, Center for Climate and Energy Solutions
Shalini Vajjhala is founder & CEO of re:focus partners, a design firm dedicated to developing integrated resilient infrastructure solutions and innovative public-private partnerships, including the RE.invest Initiative and the RE.bound Program. Prior to starting re:focus, Ms. Vajjhala served as Special Representative in the Office of Administrator Lisa Jackson at the U.S. EPA, where she led the U.S.-Brazil Joint Initiative on Urban Sustainability, EPA Deputy Assistant Administrator in the Office of International & Tribal Affairs, and Deputy Associate Director for Energy & Climate at the White House Council on Environmental Quality. She joined the Obama administration from Resources for the Future, where she was awarded a patent for her work on the Adaptation Atlas. Ms. Vajjhala received her Ph.D. in engineering & public policy and Bachelor of Architecture from Carnegie Mellon University.
Katy Maher is a Science Fellow and Resilience Project Coordinator at the Center for Climate and Energy Solutions (C2ES). She contributes to C2ES’s efforts to assess and communicate the current state of knowledge regarding climate change and its impacts, and to promote actions that strengthen climate resilience. Ms. Maher has more than eight years of experience supporting climate change impacts and adaptation projects. Prior to joining C2ES, she worked for ICF International assisting a range of clients – including the U.S. Environmental Protection Agency, Federal Highway Administration, U.S. Agency for International Development, and state and local governments – in assessing climate change risks and developing adaptation solutions. Ms. Maher also served as Chapter Science Assistant for the Social, Economic and Ethical Concepts and Methods chapter of Working Group III’s contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.
Fatima Maria Ahmad is a Solutions Fellow at the Center for Climate and Energy Solutions (C2ES) where she co-leads the National Enhanced Oil Recovery Initiative with the Great Plains Institute. Ms. Ahmad focuses on financing opportunities and policy support for emerging energy technologies, including carbon capture, use, and storage (CCUS). In a volunteer capacity, Ms. Ahmad is the Co-Chair of the American Bar Association Section of International Law International Environmental Law Committee and is the Women’s Council on Energy & the Environment Vice-Chair for Membership.
Bruce Ciallella is currently the Managing Director for HUD Programs (Office of Recovery). In this role, he oversees the Hurricane Sandy recovery effort for the New Jersey Economic Development Authority (EDA). His role includes managing the Stronger NJ Business Grant Program, the Stronger NJ Business Loan Program, the Neighborhood Community Revitalization Program, and the Energy Resilience Bank. Prior to joining the EDA, Mr. Ciallella served as Deputy Attorney General for the state of New Jersey representing the EDA and New Jersey Housing and Mortgage Finance Agency in various legal matters, including but not limited to the creation of various Hurricane Sandy programs. Furthermore, before joining the state, Mr. Ciallella was a market maker on the floor of the NASDAQ OMX PHLX trading in the oil service, homebuilder, and gold and silver sectors.
Scientists have typically been cautious when discussing the link between a single extreme weather event and climate change, preferring to focus on broader trends. Previous work, including a paper I wrote with Jay Gulledge four years ago, described a framework for how to think about the link.
But a new report from the National Academies of Sciences (NAS) is making the connection more clear by defining the relative contributions of climate change and other natural sources to the risk of individual weather events. The NAS report – an exhaustive, systematic examination of the peer-reviewed literature – finds high confidence in attribution studies linking individual extreme heat and cold events and climate change, and a more moderate confidence level for several other types of events.
Climate change is making extreme weather more likely. But individual weather events like heat waves or hurricanes are always the product of several risk factors, such as El Nino, climate change or other natural variability, akin to how a poor diet and smoking increase the risk of poor health later in life.
Extreme event attribution attempts to quantify the influence of climate change in comparison to other factors. Determining to what extent climate change strengthened or weakened the event can further our understanding of how much impact climate change is having on our weather.The NAS report assigns a confidence level to the climate impact for a variety of weather events based on three supporting lines of evidence:
- The physical mechanisms that link climate change to a particular extreme
- The length and quality of the observational record showing the baseline risk level and changes to date
- Computational climate modeling showing an increase in risk for a class of extreme event
The report finds the strongest links to climate change for extreme heat and cold, with the highest level of confidence across all three lines of evidence. Drought and extreme rainfall have medium confidence for physical understanding, observation and modeling. Extreme snowfall has medium conference for two out of three, physical understanding and modeling, while the observational record for snowfall is poor.