2040 (MMXL) will be a leap year starting on Sunday of the Gregorian calendar, the 2040th year of the Common Era (CE) and Anno Domini (AD) designations, the 40th year of the 3rd millennium, the 40th year of the 21st century, and the 1st year of the 2040s decade.
- The United Kingdom and France plan to ban the sale of all new diesel and petrol cars by this year.
- Japan will have shut down the last of its nuclear power plants.
- The United States Air Force will start an at least partial phase-out of their B-52 bombers, which by 2040 will have served for 85 years.
- Projected completion date for the Trans-European Transport Networks (TEN-T) rail corridor running from Germany to southern Italy.
- Amsterdam aims to be fossil fuel-free, powering its electric cars, trucks, boats, and buildings with energy generated by wind, solar, and biomass.
- Completion of the Northeast Corridor high-speed rail route, running from Boston to Washington, D.C.
Predicted astronomical events
- May 11 – Partial solar eclipse.
- September 8 – Planetary alignment of Mercury, Venus, Mars, Jupiter, Saturn and the crescent Moon.
- November 4 – Partial solar eclipse.
- The Great Red Spot on Jupiter's atmosphere will become circular according to calculations based on its reduction rate at present. 
- Global energy consumption will have increased by 56 percent from 2010, from 524 quadrillion British thermal units (Btu) to 820 quadrillion Btu.
- NASA predicts that by this year it will cost only tens of dollars per pound to launch humans or cargo into space.
- Space-based solar power will be commercially viable.
- Pollen counts will be more than double today's level, due to climate change.
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- "Planets for Dessert - NASA Science". Science.nasa.gov. Retrieved November 11, 2015.
- Siegel, Ethan (July 10, 2017). "Jupiter's Great Red Spot Gets Its First-Ever Close Up Today". Forbes. Retrieved May 22, 2019.
- "EIA projects world energy consumption will increase 56% by 2040 - Today in Energy - U.S. Energy Information Administration (EIA)". Eia.gov. July 25, 2013. Retrieved November 11, 2015.
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- Nancy Owano (November 15, 2011). "IAA says 'Yes We Can' to power plants in orbit". Physorg.com. Retrieved December 31, 2011.
- "The Year 2040: Double the Pollen, Double the Allergy Suffering?". NewsWise/American College of Allergy, Asthma and Immunology (ACAAI). October 30, 2012. Retrieved August 8, 2013.