An Earth Day conversation about global warming. Global warming/climate change unsurprisingly is the central topic of attention on this Earth Day 2014, and Mr. Tom Steyer of NextGen Climate has taken a leading role — to the tune of a reported $100 million — in terms of using his free-speech rights to promote the policies he supports and politicians sympathetic to his goals. In the spirit of open and collegial debate, here are five questions for Mr. Steyer.

1. There has been no temperature trend over the last 15 years; the actual record has belied the predictions of the models. The past two years have set a record for the fewest tornadoes ever for a similar period, and there has been no trend in the frequency of strong (F3 to F5) tornadoes in the United States since 1950. The number of wildfires is in a long-term decline. It has been eight years since a Category 3 or higher hurricane landed on a U.S. coast; that long a period devoid of an intense hurricane landfall has not been observed since 1900. The 2013 Atlantic hurricane season was the least active in 40 years, with zero major hurricanes. There has been no trend in the frequency or intensity of tropical cyclones, and tropical cyclone energy is near its lowest level since reliable measurements began by satellite in the 1970s. There has been no change in the long-term trend in sea level. The record of changes in the size of the Arctic ice cover is far more ambiguous than often asserted, because the satellite measurements began at the outset of the warming period from roughly 1980 through 1998. The Palmer Drought Severity Index shows no trend since 1895. Flooding in the United States over the last century has not been correlated with increases in greenhouse-gas concentrations. What systematic evidence supports the assertion that increasing atmospheric concentrations of greenhouse gases (GHG) are causing significant adverse effects?

2. If we apply the climate model developed at the National Center for Atmospheric Research (NCAR), used by both the Environmental Protection Agency and the Intergovernmental Panel on Climate Change, and employ the highest climate-sensitivity assumption of the Intergovernmental Panel on Climate Change, we find that the Obama administration’s carbon policies would reduce global temperatures in the year 2100 by about two one-hundredths of a degree. A 40 percent U.S. emissions reduction — more than double the Obama goal — would reduce temperatures by six one-hundredths of a degree. If that 40 percent reduction were to be imposed by the entire industrialized world, including China, the predicted effect is about half a degree. What economic costs should we be willing to bear to achieve such outcomes?

3. You have argued that approval of the Keystone XL pipeline would increase global GHG emissions by “1.2 billion metric tons . . . over the 50-year lifespan of the project,” yielding “potentially devastating impacts on our climate.” You must have meant 1.2 billion metric tons per year, but that estimate is almost eight times higher than the State Department figure of about 155 million metric tons per year. Global GHG emissions now are roughly 40 billion metric tons per year, so the Keystone XL contribution would be an additional 3 percent, if we use your estimate. Even if we take it as a given that a single pipeline would add 3 percent (!) to global GHG emissions, the predicted temperature effect in the NCAR climate model of that change is effectively zero. In what relevant sense would the climate impacts of Keystone XL be “potentially devastating”?

4. Global temperatures increased roughly from the middle of the 19th century (the end of the Little Ice Age) through the eruption of Krakatoa in 1883, and then from about 1910 through about 1940. They were roughly constant through about 1980, increased until 1998 (a year with a strong El Niño), and have exhibited no trend since then. How much of this long-term upward trend is anthropogenic, and how do you know?

5. You have argued repeatedly that anti-carbon policies would engender an expansion of “green” employment as an offset for the jobs lost in coal and other industries. But a shift toward (expensive) renewable energy automatically means less energy consumption in the aggregate, and the data over at least the last four decades are unambiguous: Employment and energy consumption are strongly complementary; that is, less energy means fewer jobs. Furthermore, renewables are uncompetitive and so must be subsidized heavily so as to attract investment; sooner or later those subsidies must yield higher taxes or higher energy prices or both. What are the employment implications of less energy consumption, higher taxes, and higher energy costs; and how are lower-income individuals and families likely to fare under a “green” policy regime?

Thank you in advance, Mr. Steyer, for helping to advance the debate.

— Benjamin Zycher is the John G. Searle Scholar at the American Enterprise Institute.