WASHINGTON — The Environmental Protection Agency announced Friday evening its website would be "undergoing changes" to better represent the new direction the agency is taking, triggering the removal of several agency websites containing detailed climate data and scientific information.

One of the websites that appeared to be gone had been cited to challenge statements made by the EPA's new administrator, Scott Pruitt. Another provided detailed information on the previous administration's Clean Power Plan, including fact sheets about greenhouse gas emissions on the state and local levels and how different demographic groups were affected by such emissions.

The changes came less than 24 hours before thousands of protesters were set to march in Washington and around the country in support of political action to push back against the Trump administration's rollbacks of former president Barack Obama's climate policies.

"As EPA renews its commitment to human health and clean air, land, and water, our website needs to reflect the views of the leadership of the agency," J.P. Freire, the agency's associate administrator for public affairs, said in a statement. "We want to eliminate confusion by removing outdated language first and making room to discuss how we're protecting the environment and human health by partnering with states and working within the law."

The agency also said it would carefully archive pages from the past administration.

Yet the website overhaul appears to include not only policy-related changes, but also scrutiny of a scientific Web page that has existed for nearly two decades, and that explained what climate change is and how it worked.

The EPA's extensive climate change website now redirects to a page that says "this page is being updated" and that "we are currently updating our website to reflect EPA's priorities under the leadership of President Trump and Administrator Pruitt." It also links to a full archive of how the page used to look on Jan. 19, before Trump's inauguration.

The archive notes, in a key section under the "causes of climate change," that

Recent climate changes, however, cannot be explained by natural causes alone. Research indicates that natural causes do not explain most observed warming, especially warming since the mid-20th century. Rather, it is extremely likely that human activities have been the dominant cause of that warming.

It is this language, when the site was still up, that directly contradicted Pruitt. Pruitt had argued on CNBC last month that "measuring with precision human activity on the climate is something very challenging to do and there's tremendous disagreement about the degree of impact, so no, I would not agree that it's a primary contributor to the global warming that we see."

The EPA's climate change website stated otherwise, and did so by citing findings of the United Nations' Intergovernmental Panel on Climate Change.

There had been reports early in the Trump administration that the EPA climate change website was set to be taken down, but in the end it did not happen immediately.

The page contains scientific explanations of climate change and its causes and consequences, and has existed in one form or another since the Clinton administration. At that time it was called the agency's Global Warming site.

The site has long served an informational role and sought to provide a comprehensive review of basic climate science, the effects of climate change, and how it is affecting the United States. In addition it contained information about the agency's approach to climate change and how people could take steps to lower their own contributions to climate change.

However, the site has run into political difficulties before. Under President George W. Bush, updates to the site were frozen and then required to undergo White House review. However, this process did not lead to substantive changes in scientific content.

In its press statement, the EPA said that when it comes to website changes, "the first page to be updated is a page reflecting President Trump's Executive Order on Energy Independence, which calls for a review of the so-called Clean Power Plan."

That site, www.epa.gov/cleanpowerplan, now redirects to www.epa.gov/Energy-Independence, which features an image of President Trump signing an executive order aimed at dismantling the power plant rule and other Obama-era climate regulations.

In the statement, Freire said that "language associated with the Clean Power Plan, written by the last administration, is out-of-date. Similarly, content related to climate and regulation is also under review."

Several career EPA employees, who asked for anonymity out of fear of retribution, said they were not briefed in advance about the decision to alter the agency's site.

"People are obviously unhappy," one employee said. "It is, in my opinion, the best climate education website out there."

David Doniger, director of the climate and clean air program for the advocacy group Natural Resources Defense Council, tweeted Friday, "Cleansing has begun. EPA website scrubbed of pages on "so-called" Clean Power Plan. Now only alternative facts."

Another EPA website, documenting climate change "indicators" across the United States, remained up on Friday.

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