In a recent paper ("World Scientists' Warning of a Climate Emergency"), 11,000 "concerned scientists" channeled Thomas Malthus and dropped the gauntlet in their recent study on climate change.  Apparently, Gaia is not happy with population growth.  Their imperative: "Earth's population "needs to be stabilized — and, ideally, gradually reduced — within a framework that ensures social integrity." 

The anthropogenic climate change crowd is married to ideology and a quasi-religion rather than facts and data.  A close and objective review of the data indicates that Earth is facing a depopulation problem, not an overpopulation problem.  Half the world's population has a sub-replacement fertility rate, which is 2.1 in developed nations and higher in developing countries (due to higher mortality rates).  The global fertility rate in 2017 was 2.4, steadily dropping every decade from an all-time high of 5.05 in 1964.

Taking a closer look at fertility rates by region, developed nations around the globe (i.e., G20 nations including E.U. countries, North America, China, Brazil, Japan, Australia, and South Korea), with few exceptions, have sub-replacement fertility rates.  Immigration is the driver of population growth in these countries.  Conversely, while declining the past half-century, above-replacement fertility rates are primarily found in Africa, the Middle East, Micronesia, and Western Asia.  Not surprisingly, these regions have high emigration rates to developed nations.  The countries also tend to be benefactors of U.N. wealth-transfer policies from developed nations in the stated effort to "mitigate anthropogenic climate change." 

Another key trend to analyze is the aging rates of populations.  Analysis from the Population Reference Bureau, from October of 2018, indicated that the percentage of individuals ages 65 or older in developed countries is projected to reach 27% mid-century, up from 18% now, while the percentage of adults aged 65 and older, in less developed nations, is projected to double to 14%.  The global economy is facing a pincer effect:  the fertility rate is barely sustainable at a global level and is at sub-replacement level in the developed world, and the population is aging everywhere.

These mega-trends lead to the following implications:

• Younger generations will pay continuously higher transfer payments in those countries with high entitlement obligations (i.e., G20), given sub-replacement fertility rates.  The age "pyramid" is inverting in these countries.  As such, they will have less discretionary income.
• Global GDP (~70% driven by individual consumption) growth will decline, as the global population ages, compounded by sub-replacement fertility rates across G20 nations — further exacerbated by lower discretionary income across younger generations in G20 countries. 
• The supply of labor will continue to tighten as populations age and retire and aren't backfilled.
• Politicians and global corporations are responding to these trends by pushing for higher immigration in developed nations — rationale: to help fund entitlements, drive individual consumption, and expand the labor market.
• Populist movements will continue to push back on immigration, particularly unskilled workers, given they typically represent a net cost macro-economically.

In conclusion, these 11,000 "concerned scientists" lack intellectual honesty.  From an economic perspective, this planet needs more, not fewer babies.  That ancient command — "Be fruitful and multiply" — was (and is) quite prescient.