"Lincoln’s writings speak to me ... that though we may have our differences, we are one people, and we are one nation, united by a common creed. ... Lincoln saw beyond the bloodshed and division. He saw us not only as we were, but as we might be." - President Barack Obama 
"We are confronted with the fierce urgency of now. …Over the bleached bones and jumbled residue of numerous civilizations are written the pathetic words: 'Too late.'" -Martin Luther King, Jr .
Dear President Obama,
Your words above aptly describe the greatness of Abraham Lincoln. Slavery was the moral crisis of his time, and because he fervently believed "we are one people," he took a stance which initially led to much adversity. But he rose to the challenge and the rest is history.
In a speech to Congress in 1862,  Lincoln said: "The dogmas of the quiet past are inadequate to the stormy present. The occasion is piled high with difficulty and we must rise with the occasion. As our case is new, so we must think anew and act anew."
Circumstances have conspired to place you at the presidential helm during a moment of unprecedented global crisis. Last year, we saw one of the most prominent features of our planet — as seen from space — altered beyond recognition. A huge portion of the snow and ice white of the Arctic was simply, and stunningly, gone.
Many deeply concerned about the future of life were inspired by these words in your inaugural speech: "We will respond to the threat of climate change, knowing that failure to do so would betray our children and future generations. ... Some may still deny the overwhelming judgment of science, but none can avoid the devastating impact of raging fires, and crippling drought, and more powerful storms.”
It is heartening to know you share concern about the disruptions already affecting humanity. But in the name of those future generations you seek to protect, it is essential to ask if you are fully aware that the vast danger we are facing extends well beyond these current impacts. Unless there is an unprecedented shift from our current direction, there is a point in time when the cascading consequences will begin to escalate beyond the reach of human control. If what scientists call a "tipping point" is crossed, then it will be of no avail for humanity to right its course. It will be too late.
This is why the scale of the shift away from carbon pollution is so crucial. The laws of physics do not respect any political timetable. As the suffering would sweep across all of humanity ignoring national boundaries and political affiliations, it is a time that calls out for a Lincoln-like president who can reach across all that currently divides us.
In your inaugural speech, you also shared these words: "Our obligations as Americans are not just to ourselves, but to all posterity. …That is how we will preserve our planet, commanded to our care by God."
If Creation is to be protected, there is a moral imperative to use the stature of your office to speak the truth to the American people. This crisis is not just one more "issue" but rather calls into question the very future of life as we know it. Your gift of oratory can help break through the partisan polarization and lift us all to a place where we can see our common humanity.
For those monied interests that persist in attacking the overwhelming consensus of the scientific community, there is also a moral imperative to forcefully expose the vested nature of these actions. It is a time to invoke the spirit of another American hero whom you honored on Inauguration Day — Dr. Martin Luther King, Jr. King personified the necessity to stand up to powerful forces on the wrong side of history.
In a stirring speech to the United Nations in 2009 , you said: "Our generation's response to this challenge will be judged by history, for if we fail to meet it — boldly, swiftly, and together — we risk consigning future generations to an irreversible catastrophe. …The time we have to reverse this tide is running out."
The American people have responded positively to presidents who courageously chose the moral high ground in response to soul-testing adversity. When history does judge our generation, may it be seen that we stood tall. Though "the occasion is piled high with difficulty", it is a time when — like Lincoln — we must all "rise with the occasion." As you have spoken, our "time is running out." Averting a climate catastrophe represents the greatest service you could possibly render on behalf of humanity and the most precious legacy you could possibly leave.
Gary Houser is a Christian activist on the climate crisis, recently co-producing a documentary  on the threat presented by super greenhouse gas methane now thawing in the Arctic and venting into the atmosphere.