Global Warming

Evidence and debate on climate change, temperatures, emissions, energy systems, damages, adaptation, mitigation, and climate policy. The archive brings together scientific and economic research while preserving uncertainty and competing estimates.

AI Summary. Direct carbon pricing—carbon taxes and emissions trading systems—now covers about 30% of global emissions, with most coverage coming from emissions trading systems in China and the European Union. The EU complements its system with a Carbon Border Adjustment Mechanism that prices carbon on certain high-emitting imports regardless of where they are produced.

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Bridgewater argues that carbon pricing is increasingly becoming an industrial-policy tool, with measures such as the EU’s CBAM supporting domestic producers by limiting carbon leakage, while carbon prices encourage investment in energy efficiency and industrial upgrading.

How much of global emissions does carbon pricing now cover?

Core argument: Direct carbon pricing, spanning carbon taxes and emissions trading systems, now covers roughly 30% of global emissions, with most of that coverage coming from emissions trading systems in China and the EU.

Carbon pricing schemes have continued to grow over the last few years. Some form of direct carbon pricing now covers ~30% of global emissions—spanning both carbon taxes and emissions trading systems. Most coverage comes from emissions trading systems in China and the EU, and these schemes are increasingly being adapted to fit their specific industrial policy goals. For example, as a complement to its domestic emissions trading system, the EU has started to implement a Carbon Border Adjustment Mechanism (CBAM), which imposes carbon pricing on certain high-emitting imports regardless of where they are produced. In a world of modern mercantilism, policy makers have increasingly emphasized the need for carbon pricing schemes to support—rather than constrain—industrial competitiveness.

Takeaways by Macro Roundup® AI

  1. Direct carbon pricing, spanning carbon taxes and emissions trading systems, now covers roughly 30% of global emissions, with most of that coverage coming from emissions trading systems in China and the EU.
  2. The EU has begun implementing a Carbon Border Adjustment Mechanism, which imposes carbon pricing on certain high-emitting imports regardless of where they are produced, as a complement to its domestic emissions trading system.
  3. Carbon pricing schemes are increasingly being adapted to fit specific industrial policy goals, with policy makers emphasizing that such schemes should support rather than constrain industrial competitiveness.

AI Summary. The European earth observation service reported an August global average surface air temperature of just under 62.6°F, 2.97°F above the pre-industrial baseline and on a par with the prior record, with global sea temperature at 69.93°F. Provisional US data recorded 100 consecutive days of record ocean warming.

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Global mean sea-surface temperature reached 69.9°F in August, amid 100 consecutive days of record ocean warming since early June, according to provisional NOAA data. The increase in temperature has been amplified by the El Niño cycle.

Are global air and ocean temperatures setting new records?

Core argument: The European earth observation service put August’s global average surface air temperature at 2.97°F above the pre-industrial baseline, just under 62.6°F, on a par with the previous record set in July 2023.

The European earth observation service said the global average surface air temperature in August was 2.97°F higher than the pre-industrial baseline, reaching just under 62.6°F. This put it on a par with the previous record set in July 2023. The global sea temperature in August was put at 69.93°F. This week marked 100 consecutive days of record warming since early June, according to provisional data from the US National Oceanic and Atmospheric Administration. This stretch was exceeded during the previous El Niño cycle. It is estimated that El Niño typically affects the global mean temperature by about 0.36°F, although the magnitude was likely to be larger this year because of the extent of the naturally occurring event.

Takeaways by Macro Roundup® AI

  1. The European earth observation service put August’s global average surface air temperature at 2.97°F above the pre-industrial baseline, just under 62.6°F, on a par with the previous record set in July 2023.
  2. Global sea temperature in August was put at 69.93°F, and provisional NOAA data show 100 consecutive days of record warming since early June, a stretch exceeded during the previous El Niño cycle.
  3. El Niño is estimated to affect the global mean temperature by about 0.36°F, though the magnitude was likely to be larger this year given the extent of the naturally occurring event.

AI Summary. Global fertility is likely below the replacement level needed to keep population constant in the long run, though population momentum from large cohorts of women now having children means world population will keep growing for roughly another 30 years. Unless trends change, it is projected to peak near 9bn around 2056 and then decline.

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The UN appears to systematically overestimate births; e.g. 33 of 37 countries with high-quality statistics registered fewer births in 2024 than the UN had forecast. Fernández-Villaverde and Norrick infer humanity is below replacement fertility in 2026.

Will world population keep growing even as fertility falls below replacement?

Core argument: As of 2026, humanity is likely to be below replacement fertility, with fewer births than needed to keep population constant in the long run.

In Table A1 we compare the World Population Prospects (WPP) estimates of births in 2022-2023 with the official numbers reported by several countries. [A2 shows the full sample with the deviations.] As of 2026, humanity is likely to be below the replacement fertility level: we are having fewer births than we need to keep population constant in the long run. This astonishing fact does not mean that population has stopped growing. Because of momentum effects (the large cohorts of women born two or three decades ago are having their children now, and their own parents have not died yet), world population will keep growing for another 30 years or so. But unless trends change, it will peak at roughly 9 billion around 2056 and then start falling, first slowly, then fast.

Takeaways by Macro Roundup® AI

  1. As of 2026, humanity is likely to be below replacement fertility, with fewer births than needed to keep population constant in the long run.
  2. World population is set to keep growing for roughly another 30 years because of momentum effects, as large cohorts of women born two or three decades ago have their children while their own parents are still alive.
  3. Unless trends change, world population will peak at roughly 9 billion around 2056 and then start falling, first slowly, then fast.

AI Summary. The US is projected to cut greenhouse gas emissions 27–41% below 2005 levels by 2040 under federal and state policies currently on the books. In the high-emissions scenario, reductions slow through the early 2030s and then reverse, while in the low-emissions scenario, clean technologies' cost competitiveness accelerates declines through 2040.

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Rhodium projects that under current policy, US GHG emissions will be 26–29% under the 2005 level in four years, driven by an influx of natural gas and renewable production. Their forecast for 2040 is 27-41% below the 2005 level.

How much will US greenhouse gas emissions fall under current policies?

Core argument: The US is on track to cut greenhouse gas emissions 27–41% below 2005 levels in 2040, considering all federal and state policies on the books as of June 2026.

The US is on track to reduce greenhouse gas (GHG) emissions by 27-41% below 2005 levels in 2040, considering all relevant federal and state policies on the books as of June 2026. These emissions outcomes represent divergent futures after the late 2020s. In the high-emissions scenario, the emissions reductions that have characterized the last 20 years slow through the early 2030s before reversing direction altogether, with growing emissions through most of that decade. In the low-emissions case, the economic competitiveness of clean technologies relative to fossil incumbents, alongside an imperative for “speed-to-power” for large loads, continues—and accelerates—GHG emission declines through 2040.

Takeaways by Macro Roundup® AI

  1. The US is on track to cut greenhouse gas emissions 27–41% below 2005 levels in 2040, considering all federal and state policies on the books as of June 2026.
  2. In the high-emissions scenario, the emissions declines of the past 20 years slow through the early 2030s and then reverse, with US emissions growing through most of that decade.
  3. In the low-emissions scenario, the economic competitiveness of clean technologies relative to fossil incumbents and a "speed-to-power" imperative for large loads accelerate US emissions declines through 2040.

AI Summary. Running standard demographic models—including the Cohort-Component, United Nations World Population Prospects, Lee-Carter, and Lotka-Volterra approaches—across all plausible analytical choices yields a wide range of possible global population outcomes for 2050 and 2075. The authors argue that presenting a single population trajectory hides the compounding uncertainty inherent in such projections.

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Simulation of the decision chain yielding projections of world population in 2050 that range from 6 to 14B suggests most of the variance in demographic forecasts arises not from parameter uncertainty or data randomness but from model choice.

How much uncertainty do single-trajectory population projections hide?

Core argument: Propagating all plausible analytical choices through global population projections to 2050 and 2075 yields wide overall uncertainty distributions, with the Cohort-Component, UN World Population Prospects, Lee-Carter and Lotka-Volterra models showing distinct sensitivities and outcomes.

We explore demographic predictions by propagating all plausible choices that can be made during the analysis through the modelling process. This approach involves navigating the so-called ’garden of forking paths’—mimicking in silico what would happen if multiple investigators were to examine the same problem. For this, we now abandon [the Chinese government mathematician] Song Jian’s ‘historic’ model and turn to models currently in use: the Cohort-Component and UN WPP models, the Lee-Carter model and the Lotka-Volterra model. Note that in standard use, these tools are used in isolation, see e.g. the FAO’s How to Feed the World in 2050, resting on a single UN WPP population trajectory shielding the reader from the compounding effect of their uncertainty. Unsurprisingly, the exercise capturing the modelling of the modelling process for global population projections to 2050 and 2075 reveals distinct characteristics regarding the sensitivity and projection outcomes of the different models. Once abandoned the straitjacket of Song’s approach, uncertainty is free to manifest itself. The overall uncertainty distributions of the projected populations show a wide range of possible outcomes, reflecting the inherent uncertainties in demographic projections.

Takeaways by Macro Roundup® AI

  1. Propagating all plausible analytical choices through global population projections to 2050 and 2075 yields wide overall uncertainty distributions, with the Cohort-Component, UN World Population Prospects, Lee-Carter and Lotka-Volterra models showing distinct sensitivities and outcomes.
  2. Standard demographic practice uses these projection models in isolation, as in the FAO's How to Feed the World in 2050, which rests on a single UN World Population Prospects trajectory and shields readers from the compounding effect of their uncertainty.
  3. Abandoning Song Jian's historic model and navigating the "garden of forking paths"—mimicking in silico what would happen if multiple investigators examined the same problem—allows uncertainty in demographic projections to manifest itself.

AI Summary. Global sea temperatures reached their second highest level on record for the month of April, with the European Union's Copernicus Climate Change Service reporting record sea-surface temperatures across much of the tropical Pacific. Scientists say this raises concerns that an El Niño warming cycle is forming, which would temporarily accelerate global air temperature rise and intensify fires, floods and droughts.

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April’s global ocean temperatures rose to their second-highest level on record, suggesting a brewing El Niño warming cycle. April temperatures were just shy of their level in 2024, which was also an El Niño year.

Are record ocean temperatures signaling more extreme weather ahead?

Core argument: Global average sea-surface temperatures for non-polar oceans reached 21°C (69.8°F) in April, just below the record 21.04°C (69.9°F) set in April 2024 during the last El Niño event.

Sea temperatures around the world were the second highest on record for the month of April, stoking concerns among scientists that an El Niño warming cycle is brewing that would intensify extreme weather. The naturally occurring El Niño weather phenomenon, where water temperatures in the central and eastern tropical Pacific Ocean become significantly warmer, temporarily accelerates the rise in global air temperature, resulting in the spread of fires, floods and droughts. The EU’s Copernicus Climate Change Service reported record sea-surface temperatures across much of the tropical Pacific in April, while the global average for non-polar oceans reached 21°C [69.8°F]— just shy of the 21.04°C [69.9°F] record set in April 2024 during the last El Niño event.

Takeaways by Macro Roundup® AI

  1. Global average sea-surface temperatures for non-polar oceans reached 21°C (69.8°F) in April, just below the record 21.04°C (69.9°F) set in April 2024 during the last El Niño event.
  2. The EU's Copernicus Climate Change Service reported record sea-surface temperatures across much of the tropical Pacific in April, stoking scientists' concerns that an El Niño warming cycle is brewing.
  3. El Niño, in which central and eastern tropical Pacific waters become significantly warmer, temporarily accelerates the rise in global air temperature and results in the spread of fires, floods and droughts.

AI Summary. Lower fertility cannot meaningfully reduce mid-century emissions because of timing: most people alive in 2050 have already been born, with United Nations projections implying about 75% of the 2050 US population will be over age 24. A 10% decline in births would cut the 2050 population by only about 2.5%, mostly children whose consumption and emissions are low.

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Kuruc argues fertility changes reduce population far too slowly to affect near-term climate goals – particularly reducing carbon emissions. Further, smaller and older populations will mean greater fiscal constraints on environmental initiatives.

Can lower birth rates meaningfully reduce mid-century emissions?

Core argument: United Nations 2024 projections expect about 75% of the U.S. population in 2050 to be over age 24 and thus born before 2026, so fertility changes can affect only the remaining 25% of the population pyramid.

The reason that low fertility will not reduce long-run climate change is simple: timing. The timelines over which the world is aiming to substantially curtail emissions do not line up with the timelines over which fertility impacts the size of the population. It is too late for changes in fertility to make a large difference in population sizes this century, and by the end of this century, it will be too late for population changes to make a large difference to eventual warming. A large majority of the people who will be alive in 2050—a focal year in climate discussions—have already been born. Demographic projections expect that about 75% of the United States population in 2050 will be over the age of 24, and hence, born prior to 2026 (United Nations 2024). Even an immediate change in fertility can only affect the 25 percent of the population pyramid that has not yet been born, implying that, for example, a 10% decline in births would produce only a 2.5% decline in the size of the overall 2050 population. Moreover, these missing individuals would be mostly children—too young to have entered the workforce, when their income, consumption, and emissions peak. So, any realistic decline in near-term births would have a trivial impact on mid-century emissions.

Takeaways by Macro Roundup® AI

  1. United Nations 2024 projections expect about 75% of the U.S. population in 2050 to be over age 24 and thus born before 2026, so fertility changes can affect only the remaining 25% of the population pyramid.
  2. A 10% decline in births would produce only a 2.5% decline in the overall 2050 population, and those missing individuals would mostly be children, too young to have entered the workforce, when income, consumption, and emissions peak.
  3. The environmental case for low fertility turns on timing: it is too late for fertility changes to make a large difference in population size this century, and by the end of the century population changes will matter little for eventual warming.

AI Summary. Insurance broker Aon reports global insured losses from natural disasters exceeded $127bn, with more than $100bn in the US, led by the Los Angeles wildfires, while total global economic losses from disasters reached about $260bn. More than half of those economic losses were uninsured, reflecting persistent coverage gaps in emerging markets.

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$100B of the $127B total global insured losses due to natural disasters in 2025 were in the US, according to an Aon report, ~$58B of which were caused by the Los Angeles fires. Overall global economic losses from disasters in 2025 totaled $260B.

How large were global insured and uninsured natural disaster losses?

Core argument: Global insured losses from natural disasters exceeded $127bn in 2025, with more than $100bn occurring in the US after the Los Angeles fires, according to insurance broker Aon.

Global insured losses of more than $127bn from natural disasters were dominated by more than $100bn occurring in the US in 2025 after the Los Angeles fires, according to a new industry report on climate and other extreme events. Overall global economic losses stemming from disasters, including thunderstorms and earthquakes, totalled about $260bn, according to the review by insurance broker Aon. But more than half of those losses remain not covered by insurance, highlighting the persistence of inadequate coverage in emerging markets, it said. “Extreme weather events are becoming more frequent and unpredictable, affecting new geographies and sectors, and challenging long-held assumptions about resilience,” wrote Greg Case, Aon chief executive. “Weather exposures are rising,” he noted. Insured losses from climate disasters were 27% higher than the long-term average since 2000.

Takeaways by Macro Roundup® AI

  1. Global insured losses from natural disasters exceeded $127bn in 2025, with more than $100bn occurring in the US after the Los Angeles fires, according to insurance broker Aon.
  2. Aon puts total global economic losses from disasters, including thunderstorms and earthquakes, at about $260bn, with more than half uninsured, highlighting the persistence of inadequate coverage in emerging markets.
  3. Insured losses from climate disasters ran 27% above the long-term average since 2000, and Aon chief executive Greg Case wrote that extreme weather events are becoming more frequent and unpredictable, affecting new geographies and sectors.