Science envoy to the US State Department Daniel Kammen who resigned in a public letter that went viral has said he did so because "facts matter".

Mr Kammen, a professor at the University of California - Berkeley, told The Independent that the only way for the scientific community to operate in what some former government science advisors during the Trump administration have called an environment of hostility towards evidence and data is "to be clear that facts do matter, and to show that open and inclusive research and action can prevail."

His letter of resignation pointed to Mr Trump's response to the violence in Charlottesville, Virginia during which Ku Klux Klan members, neo-Nazis, and other white supremacists protested the removal of a statue of Civil War Confederate General Robert E Lee.

Counter-protesters were present to oppose keeping the statue because they saw it as a monument to a losing side in the bloodiest war in America and a monument to hundreds of years of brutal slavery.

Mr Trump has maintained his thought that "many sides" were responsible for the violence that resulted in three deaths - two Virginia State Police officers in a helicopter accident and a counter-protester who was killed after a car rammed into a crowd - and that there were "innocent" protesters who wanted to keep the statue to preserve history who were "treated very badly" by the media.

He did condemn the hate groups but many CEOs and members of various presidential councils felt it was too little, too late.

Mr Kammen wrote in his letter: "Your response to Charlottesville enables racism, sexism, & harms our country and planet."

He posted his resignation letter in full on Twitter, where it was quickly shared tens of thousands of times. The first letters of each paragraph read: "IMPEACH," his apparent message about Mr Trump's presidency.

Mr Kammen said he was inspired by the members of the Presidential Committee on the Arts and the Humanities, who resigned with a letter spelling the message "RESIST" with the first letter of each paragraph after the President's response to Charlottesville.

The Director of the Renewable and Appropriate Energy Laboratory at UC- Berkeley, Mr Kammen had been appointed in 2010 as the very first Environment and Climate Partnership for the Americas (ECPA) Fellow at the State Department and worked on a variety of issues including climate change.

He said he did not immediately resign from his consulting post after Mr Trump announced the US withdrawal from the Paris Agreement on climate change because "left the door open after pulling the US out to return" or re-negotiate the deal, which nearly 200 countries signed in order to reduce carbon emissions and help poorer countries adapt to an already-changed planet.

Violence on the streets of Charlottesville Show all 9 1 /9 Violence on the streets of Charlottesville Violence on the streets of Charlottesville Protesters clash and several are injured White nationalist demonstrators clash with counter demonstrators at the entrance to Lee Park in Charlottesville, Virginia. A state of emergency is declared, August 12 2017 Violence on the streets of Charlottesville Trump supporters at the protest A white nationalist demonstrator walks into Lee Park in Charlottesville, Va., Saturday, Aug. 12, 2017. Hundreds of people chanted, threw punches, hurled water bottles and unleashed chemical sprays on each other Saturday after violence erupted at a white nationalist rally in Virginia. AP Photo Violence on the streets of Charlottesville State police stand ready in riot gear Virginia State Police cordon off an area around the site where a car ran into a group of protesters after a white nationalist rally in Charlottesville, Virginia AP Photo Violence on the streets of Charlottesville Militia armed with assault rifles White nationalists, neo-Nazis and members of the 'alt-right' with body armor and combat weapons evacuate comrades who were pepper sprayed after the 'Unite the Right' rally was declared a unlawful gathering by Virginia State Police. Militia members marched through the city earlier in the day, armed with assault rifles. Getty Images Violence on the streets of Charlottesville Statue of Confederate General Robert E Lee The statue of Confederate General Robert E. Lee stands behind a crowd of hundreds of white nationalists, neo-Nazis and members of the 'alt-right' during the 'Unite the Right' rally 12 August 2017 in Charlottesville, Virginia. They are protesting the removal of the statue from Emancipation Park in the city. Getty Images Violence on the streets of Charlottesville Racial tensions sparked the violence White nationalists, neo-Nazis and members of the 'alt-right' exchange insults with counter-protesters as they attempt to guard the entrance to Lee Park during the 'Unite the Right' rally Getty Violence on the streets of Charlottesville A car plows through protesters A vehicle drives into a group of protesters demonstrating against a white nationalist rally in Charlottesville, Virginia. The incident resulted in multiple injuries, some life-threatening, and one death. AP Photo Violence on the streets of Charlottesville Rescue personnel help injured people after a car ran into a large group of protesters after an white nationalist rally in Charlottesville, Virginia AP Photo Violence on the streets of Charlottesville President Donald Trump speaks about the ongoing situation in Charlottesville, Virginia from his golf club in Bedminster, New Jersey. He spoke about "loyalty" and "healing wounds" left by decades of racism.

However, Mr Kammen noted: "while I disagree with that decision, if he were to have engaged, or had [Secretary of State Rex] Tillerson do so, I would be displeased, but would take a wait and see. There seems to be no re-engagment taking place."

In fact, at least three countries - Germany, Italy, and France - were quick to respond to Mr Trump's announcement and said re-negotiation was not possible. Environmental Protection Agency Chief Scott Pruitt may have increased tensions when he insisted that parties must come to the US if they want America in the agreement.

Mr Kammen wrote in the letter that the President's "decision to abdicate the leadership opportunities and job creation benefits" of the Paris Agreement was "not acceptable".

He said that the President has "is justifying and emboldening extremists who threaten other communities. That is not acceptable leadership and impact both domestic issues, and the international level of tolerance, or, actually, intolerance."

Mr Kammen explained that kind of leadership makes his "role as a science envoy charged to facilitate collaborations" between the US, Middle East, and Africa that much more difficult.