The stock of greenhouse gases in the atmosphere will determine the degree of warming around the world, and thus the degree of harm from more extreme weather events, droughts, floods, sea level rise and more. Scientists tell us that if we are to have a reasonable chance to limit average temperature rise to 2 degrees C (3.6 degrees F), the upper end of the acceptable limit, there is only so much greenhouse gas we can emit. Once we have reached this level, we must totally stop adding new emissions to the atmosphere.
At current rates, our remaining emissions' "allowance" will be used up well before 2050, implying we must get ready now for a decarbonized economy. If we immediately begin to reduce emissions, we will have a few more decades before we need to fully decarbonize. Either way, global emissions will need to be net zero this century.
The G7 commitment to a medium-term target (a reduction of 40 to 70 percent by 2050) and long-term, full decarbonization this century is exactly the kind of leadership that is needed.
In making this commitment, governments are finally responding to the global corporations that have been pleading for policy clarity. One group of leading CEOs (the so-called B-Team) have called for full decarbonization of energy by 2050. More than 1,000 corporations have signed a commitment to support a price on carbon. Another group of 100 major companies have committed to sourcing only renewable energy, with top global brands like Walmart and IKEA pledging to power their companies with only non-fossil sources. Others – including Facebook, Unilever and General Motors – are signing up to the Corporate Renewable Energy Buyers Principles, which assists companies in the transition to low-carbon energy.
There is growing recognition that these actions will benefit our economy, our citizens, our competitiveness and our quality of life. As much as 90 percent of what we need to do to address climate change is compatible with accelerating economic development. And the United States is well-placed to lead in driving this transition. The good news is that we don't have to choose between climate action and a strong economy. Last year, the New Climate Economy report reaffirmed that smart climate policy goes hand-in-hand with economic opportunity.
Momentum for action is building. Two weeks ago, I had the extraordinary honor of joining business leaders and policymakers to discuss the need for climate action with Pope Francis and leaders of the Catholic Church at the Vatican. We exchanged ideas about our shared vision to protect the Earth and its people.
This week, Francis issued a major encyclical to bishops. The message to the world's 1.2 billion Roman Catholics adds a major moral voice to the debate, stressing that climate change disproportionately affects the world's poor. We all share in the responsibility to ensure all people have the opportunity for healthy and prosperous lives.
The pieces of the puzzle are falling into place: The scientific, economic and moral case all point to the need for a strong international agreement and greater national and sub-national action. The G7 has wisely joined the growing chorus.
2015 holds the potential as a major turning point in history, pointing us toward a safer and economically secure future. World leaders should seize the opportunity to make sure it does.