“I have no problem with setting a goal of zero emissions by 2050. I have a serious problem with pretending we know how to get there.” — Vaclav Smil
The concentration of carbon dioxide in Earth’s atmosphere has risen from approximately 280 parts per million (ppm) in pre-industrial times to approximately 420 ppm today. This represents a 50% increase in 150 years — a change that would have taken tens of thousands of years under natural conditions.
Global average surface temperature has risen by approximately 1.2°C since pre-industrial times. The Intergovernmental Panel on Climate Change (IPCC) projects that without significant emissions reductions, temperatures could rise 2.5°C-4°C by 2100.
Global CO2 emissions from energy and industry: approximately 37 billion tons per year (as of recent data)
Top emitters by country (approximate share of global total):
Per capita emissions (tons of CO2 per person per year):
These per capita numbers are crucial. China’s total emissions are larger than the US, but its per-capita emissions are barely above the global average. The historical responsibility for accumulated CO2 in the atmosphere is concentrated in wealthy countries that industrialized first.
The public discourse about decarbonization focuses disproportionately on electricity generation and personal cars — sectors where solutions are well-advanced. Smil insists on examining the sectors where decarbonization is genuinely difficult.
Smil identifies four materials that modern civilization cannot function without — and that are extremely difficult to produce without fossil fuels:
Steel — requires iron ore reduction using either coking coal or (in the future) hydrogen. Steel production emits approximately 1.8 billion tons of CO2 annually — about 5% of global emissions. Green steel using hydrogen is technically possible but currently 2-3 times more expensive.
Cement — the production of calcium silicate clinker (the key ingredient) chemically releases CO2 regardless of the energy source used. Cement production contributes approximately 8% of global CO2 emissions. Carbon capture is possible but adds significant cost.
Plastics — currently made almost entirely from petrochemical feedstocks. Replacing fossil fuel feedstocks with bio-based alternatives at the required scale (400 million tons per year) remains enormously challenging.
Ammonia (fertilizer) — the Haber-Bosch process uses natural gas both as energy and as hydrogen feedstock. Replacing it with green hydrogen is technically feasible but currently far more expensive.
Decarbonizing these four sectors alone — which together account for roughly 17-20% of global CO2 — requires technologies that are available in demonstration but not at commercial scale.
The term “net zero” — meaning that human activities add no net CO2 to the atmosphere — has become ubiquitous in corporate and government commitments. Smil insists on examining what it actually requires.
To reach net zero by 2050:
This is not an argument against trying. It is an argument for honesty about the scale of the transformation required, the technologies that must be developed, and the time it will take.
Smil’s consistent message is not pessimism — it is the demand for what he calls “rational optimism”: set ambitious goals, but build them on a realistic understanding of the systems, materials, and timescales involved.
What would you need to believe about energy technology, political will, and global coordination to be confident that net zero by 2050 is achievable? Which of those beliefs is best supported by historical evidence?