Editor's note: Adam Markham, director of climate impacts for the Union of Concerned Scientists' Climate and Energy Program and a co-author of the report “National Landmarks at Risk," has written the following rebuttal to Dr. Daniel B. Botkin's column on climate change and his thoughts on what is, and isn't, driving it.

My colleagues and I wanted to respond to a recent column by Dr. Daniel Botkin that criticized a report we wrote regarding the threats climate change poses to historic places and landmarks in the United States.

Dr. Botkin challenged the basic science on which we based our report, yet in February 2014, the U.S. National Academy of Sciences and the UK Royal Society released a joint publication in which they stated: “Scientists know that recent climate change is largely caused by human activities from an understanding of basic physics, comparing observations with models, and fingerprinting the basic patterns of climate change caused by different human and natural influences.”

While Dr. Botkin rightly notes that sea level rise has been a problem for a long time, he doesn’t acknowledge that the rate of sea level rise is increasing as the ocean expands and glaciers and ice sheets melt due to global warming. Sea level is projected to continue increasing, threatening nearly all coastal areas. The future rate of change depends on how much heat-trapping emissions we release into the atmosphere.

Dr. Botkin also points to hurricane landfall statistics to dismiss our conclusions about flooding at historic sites. But all storms, not just hurricanes, are made more destructive by higher seas. Some of the sites we examined, in fact, are at risk of flooding, or already experiencing it, during regular high tides because sea levels are rising. Downtown Annapolis, for instance, is expected to see 200 tidal floods a year by 2030.

In the report, we also point to the problem of coastal erosion, which can be exacerbated by higher water levels even if storm frequencies remain the same. For instance, in Alaska warming has caused the loss of the seasonal sea ice that used to protect the coast from erosion in winter storms. As a consequence, native villages such as Kivalina and Shishmaref will have to relocate to protect their residents, and archaeological sites that are more than 4,000 years old are being washed away.

Dr. Botkin also cited national fire statistics in his critique. While wildfires occur all over the United States, they are most prevalent in the U.S. West, where they have been increasing as the climate has warmed. While the Western wildfire season lasted about 5 months in the 1970s, it has now expanded to 7 months. Hotter and drier conditions in the U.S. West, along with shorter winters and lowered snowpack, are helping create the conditions that lead to larger fires. The scientific evidence is clear that climatic conditions are the primary factor driving changes in fire activity in the region. In our report, we focused on Western sites that face substantial risks from large and intense wildfires.

Archaeologists at globally important sites including Bandelier National Monument and Mesa Verde National Park have expressed deep concern about the impacts of larger fires and extreme rainfall events on thousands of ancient Pueblo sites.

Let’s also clear up how we wrote our report. The report was drafted by UCS staff, including a scientist who has been studying climate change for years. We carried out extensive literature reviews for each of the sites highlighted, drawing on the latest peer-reviewed publications and technical reports. In the process, we also interviewed many site managers and field scientists familiar with the sites about which we wrote. The final text and case studies were then reviewed by more climate scientists, archaeologists, historians and, indeed, many of the men and women who manage and preserve the historic sites we highlighted as vulnerable to the effects of climate change. (As an aside, Dr. Botkin erroneously described my colleague Kate Cell, a senior outreach coordinator at UCS as a fundraiser. In addition to other excellent work she did on the report, Ms. Cell also helped organize this exhaustive review process.)

The people in charge of these sites are, in many cases, already dealing with climate change. To cite one example, NASA is contemplating a ‘planned retreat’ from sea-level rise and land subsidence at Wallops Island in Virginia, where some of the nation’s early experiments in rocketry took place. Major efforts are also underway to protect the shoreline at the original colonial settlement site at Jamestown, Virginia due to erosion and flooding exacerbated by rising water levels.

Further, the National Park Service runs a climate change response program and has adopted an ambitious climate change action plan. Interior Secretary Sally Jewell who has traveled widely in the national parks since she was appointed has said “everywhere I’ve gone the impact of climate change has been very evident”  With regard to historic sites, a recent policy memo from National Park Service Director Jon Jarvis stated “Climate change poses an especially acute problem for managing cultural resources because they are unique and irreplaceable -- once lost they are lost forever”.

The parks themselves are also a rich source of information about our changing climate. As one study by National Park Service climate scientist, Patrick Gonzalez noted, “Field measurements in national parks have detected glacial melt, decreased snowfall and snowpack, earlier spring warmth and streamflow, sea-level rise, increased conifer mortality, and shifts of vegetation biomes, small-mammal ranges, and winter bird ranges. Analyses attribute these impacts to climate change.”

Ultimately, Dr. Botkin’s column was less about our report and more of a criticism of the science used by the Intergovernmental Panel on Climate Change (IPCC), one of the authoritative climate science assessments upon which we relied.

The IPCC is the largest scientific assessment body in the world. Its reports are commissioned by the United Nations and the World Meteorological Organisation, written by scientists, scrutinized through an exhaustive public comment process, and approved by member countries.

We used many other sources in addition to the IPCC, including the National Climate Assessment. Published in May 2014, it is the most comprehensive review of climate science ever carried out for the United States. It concluded that “global climate is changing and this change is apparent across a wide range of observations. The global warming of the past 50 years is primarily due to human activities.”

The National Climate Assessment is produced by an independent advisory committee and finalized by more than a dozen federal science agencies, including the Department of the Interior, which houses the National Park Service. Its reports are authorized by Congress, open to public comment, and are considered the definitive guide to climate change in the United States.

Dr. Botkin is right to assert that climate change is not the only concern at the parks or sites we wrote about in our report. But it is happening and it makes many of the problems parks are already dealing with – including wildfires and flooding – worse than they would be otherwise.

Thankfully, the people in charge of these sites are paying close attention to the science. They are seeking to reduce climate risk and planning for long-term resilience because these sites are part of our heritage. These men and women are stewards, and they want to enable our children and grandchildren to enjoy these sites, even as the climate changes rapidly around us.