In 2015, I was in Paris as an observer of the UN climate negotiations and part of the University of Colorado delegation. The Paris Agreement committed to reduce greenhouse gas (GHG) emissions across the world that contribute to temperature rise — often considered the fingerprint of climate change — and hold the increase “to well below 2 C above pre-industrial levels” and pursue efforts “to limit the temperature increase to 1.5 C above pre-industrial levels.”

These targets emerged through analysis of how to avoid the most severe impacts of climate change. They have been guided by periodic reports from the UN Intergovernmental Panel on Climate Change (IPCC). I was a Contributing Author to the most recent set of IPCC reports as a subject matter expert on policy, communication and public engagement. These also harmonize efforts with the 1992 UN Framework Convention on Climate Change (UNFCCC) where Article 2 centrally calls for “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.” UNFCCC was signed by US President George H.W. Bush and was ratified by the U.S. Senate shortly thereafter. I was 18 years old in 1992.

The 2015 Paris Agreement was signed by 196 UN parties. At that time, my kids were 10 and 13. On November 4, 2016, the Obama Administration agreed to reduce GHG emissions by 26-28% below 2005 levels by 2025. At that time, carbon dioxide (CO2) levels in the atmosphere (the dominant GHG) were about 400 parts per million (ppm), 120 ppm above preindustrial levels. 2015 clocked in at about 0.9 C (1.6 F) above the 20th-century average.

Then in 2016, Trump became president. By June 2017 his administration announced it was withdrawing from the Paris Agreement. Yet in the Agreement, Article 28 states that countries can withdraw only three years from their first commitment date, and from that point, it takes another year to take effect. So on November 4, 2019, the Trump Administration officially repeated the notice to withdraw. Effectively then on November 4, 2020 — one day after the 2020 US presidential election of Joe Biden — the U.S. withdrew from the Paris Agreement. At that point in 2020, CO2 levels in the atmosphere were about 414 ppm. 2020 was just coming in at about 1 C or 1.8 F above the 20th-century average.

Soon after Joe Biden was sworn in as President in 2021, he rejoined and there was a gap of 107 days that the U.S. was effectively withdrawn. At that time — recognizing ongoing worrisome climate change trends — the Biden Administration set a more ambitious commitment to reduce GHG emissions by 50-52% below 2005 by 2030. Part of Biden’s rationale was that this U.S. commitment — as the world’s largest historical emitter of GHGs, now contributing 13% overall — more effectively aligned with the Paris Agreement goal to limit warming to 1.5 C (2.7 F).

Here in 2025, U.S. emissions have come down 18% from 2005 with policy tools like those in the 2022 Inflation Reduction Act rolling out. At the end of 2024, Rhodium Group estimated that the U.S. was on track to reduce emissions 38-56% below 2005 levels by 2035. The just completed year 2024 also registered at about 1.3 C (2.3 F) above the 20th century average — the warmest year in recorded history — with 426ppm CO2 in the atmosphere. My “kids” are now both adults, ages 19 and 22.

Now on Monday — just after the inauguration — Trump announced another U.S. withdrawal from the Paris Agreement, joining only Iran, Libya and Yemen as the only defectors from this international agreement. This time, the three-year period in Article 28 does not apply, but the one-year period does. That means that the U.S. will effectively withdraw by January 20, 2026. This time, instead of 107 days, the non-participation period will likely be on the order of years.

In 2050, my adult children will be about my age as I write this now. No matter the wavering we continue to see in U.S. leadership, the planet will continue to warm as we load it with GHGs. Globally, there is no time to waste, there is no more time for resignation. The planet keeps the score. In the forfeiting of U.S. Trump administration leadership, responsibility falls now more centrally on other world leaders, and on subnational jurisdictions and each of us to continue to significantly decarbonize our industries and society.

Email: mboykoff@gmail.com.