The climate change debate continues.

[onetrack]

I'm a little puzzled as to how scientists get really precise CO2 measurements from 5000 and 6000 years ago, when they didn't have their current instruments there.

[onetrack]

There is also scientific proof that the Earth suffers from mega-droughts about every 1000 years. These mega-droughts have been blamed for civilisation collapse in some regions, where entire civilisations just disappeared.

 

If there are mega-droughts on a regular basis, this indicates long-term cyclical events in the climate, such as extreme heat periods, extreme rainfall periods, and extreme storms.

Yet, the climate scientists tell us all these previously-mentioned events are simply the result of GW. I think the whole story is a lot more complex.

 

We certainly have pumped a lot of pollutants into our atmosphere since the start of the Industrial Revolution, and anything we can do to moderate that, must be advantageous.

[octave]

58 minutes ago, onetrack said:

I'm a little puzzled as to how scientists get really precise CO2 measurements from 5000 and 6000 years ago, when they didn't have their current instruments there.

Drilling ice cores. The deeper they drill the further back in time they go. The gas in these ice cores is a sample of the atmosphere at the time.

 

https://climate.mit.edu/ask-mit/how-do-we-know-how-much-co2-was-atmosphere-hundreds-years-ago

Edited 15 hours ago by octave

[pmccarthy]

There are several studies that challenge the ice core data, and show that it is incompatible with actual conditions. For example https://www.researchgate.net/publication/396389619_Historical_CO_levels_in_periods_of_global_greening

 

 

[octave]

Within science there are often a range of studies.  Over time peer review and further studies make things clearer.  As a layperson I go with the majority of science sources.  Obviously I can't read and analyse this paper myself and I suspect you can't either.

I did look at what other scientists say about this study

 

 

 

 

 

 

Article: Historical CO₂ levels in periods of global greening
Author: Frans J. Schrijver (2025)

Main question

The paper asks whether today's increase in plant growth ("global greening") caused by rising atmospheric CO₂ implies that past periods with equally lush or greener vegetation must also have had higher atmospheric CO₂ concentrations than those shown in Antarctic ice-core records. SScience of climate change

How the author approaches the problem

The paper:

• Starts from evidence that global terrestrial plant productivity (Gross Primary Production, or GPP) has increased by roughly 30% since 1900, largely attributed to CO₂ fertilization. SScience of climate change+1
• Uses Mitscherlich's Law (a mathematical model describing diminishing returns in plant growth with increasing nutrients) to estimate how GPP changes with atmospheric CO₂.
• Applies the model to historical periods believed to have been at least as green as today, including:
  • the Holocene Climate Optimum
  • the Eemian Interglacial
  • the Miocene
• Compares the CO₂ concentrations that the model suggests would be required with CO₂ estimates from Antarctic ice cores. SScience of climate change

Main conclusions

The author concludes that:

• If modern greening is primarily driven by higher CO₂,
• and if earlier warm periods were similarly or more vegetated,
• then atmospheric CO₂ during those periods may have been substantially higher than the <300 ppm values indicated by Antarctic ice-core reconstructions.

The paper therefore argues that the conventional interpretation of long-term ice-core CO₂ records may underestimate past atmospheric CO₂ during certain warm intervals. SScience of climate change

Significance

The paper suggests that if its analysis is correct:

• historical CO₂ variability may have been larger than generally accepted;
• climate sensitivity to CO₂ could differ from current mainstream estimates;
• additional evidence beyond Antarctic ice cores should be considered when reconstructing ancient atmospheric CO₂. SScience of climate change

Important context

This paper presents an argument that differs from the prevailing scientific consensus.

The mainstream view, reflected in assessments by the Intergovernmental Panel on Climate Change and much of the paleoclimate literature, is that:

• Antarctic ice cores provide reliable atmospheric CO₂ records over the past ~800,000 years.
• Multiple independent proxies (marine sediments, fossil plant stomata, boron isotopes, and others) broadly support the conclusion that pre-industrial CO₂ remained around 180–300 ppm during that interval, despite uncertainties for much older periods. GGMD+2

The Schrijver paper challenges this interpretation by reasoning from vegetation productivity rather than by presenting new direct CO₂ measurements. As a result, its conclusions are not widely accepted and should be viewed as a hypothesis that would require corroboration from multiple independent lines of evidence.

Edited 9 hours ago by octave

[octave]

A deeper analysis

 

The paper, "Historical CO₂ levels in periods of global greening" by Frans J. Schrijver, was published in the journal Science of Climate Change. The author is an independent researcher, and the journal is not widely regarded as a leading journal in paleoclimate or atmospheric science. The paper contains no new measurements—it is a modelling exercise based on previously published datasets. (Science of climate change)

That doesn't automatically make it wrong, but extraordinary claims require strong evidence.

---

What is the paper actually arguing?

The argument goes something like this:

1. Earth today is greener than it used to be because higher CO₂ stimulates plant growth.

2. There have supposedly been periods in the past with similar or greater greening.

3. Therefore CO₂ must also have been much higher in those periods.

4. Since Antarctic ice cores don't show these higher CO₂ levels, the ice cores must be wrong.

Notice that this is not direct evidence that the ice cores are inaccurate.

It is an indirect inference:

"My model predicts higher CO₂, therefore the measurements must be wrong."

That is a much weaker form of evidence.

---

The biggest flaw: greenness does not uniquely determine CO₂

The paper effectively assumes

more vegetation = higher atmospheric CO₂.

But ecologists have known for decades that plant productivity depends on many variables:

• rainfall

• temperature

• sunlight

• soil nutrients

• nitrogen

• phosphorus

• disturbance (fire)

• land use

• length of growing season

• species composition

CO₂ is only one factor.

The paper acknowledges diminishing returns from CO₂ fertilisation, but still treats CO₂ as the dominant explanation for high global primary productivity. That assumption is not demonstrated. (Science of climate change)

---

It ignores multiple independent CO₂ records

This is probably the strongest criticism.

Ice cores are not the only evidence for past CO₂.

Scientists also use:

• marine sediments

• boron isotopes

• stomatal density in fossil leaves

• paleosols

• alkenones

• isotopic carbon chemistry

These completely independent methods broadly agree with the Antarctic ice-core record over overlapping time periods.

A recent Nature study extending atmospheric CO₂ measurements back to about 3 million years found broadly stable CO₂ levels consistent with existing paleoclimate understanding rather than the large fluctuations proposed by ice-core critics. (Nature)

If the ice cores were fundamentally wrong, we'd expect these independent methods to disagree. They generally don't.

---

The paper revives criticisms that have already been examined

The paper relies heavily on arguments from:

• Zbigniew Jaworowski

• Ernst-Georg Beck

• Hermann Harde

These authors have argued for years that:

• CO₂ diffuses through ice

• meltwater alters trapped air

• ice cores smooth or destroy past CO₂ peaks

These criticisms have been investigated extensively.

Scientists agree on one point:

Ice cores smooth rapid year-to-year fluctuations.

They do not preserve every individual year's atmospheric CO₂ exactly.

That is well understood.

But smoothing is very different from inventing a completely false average.

The gas age distribution in Antarctic ice is modelled and measured.

Researchers know approximately how much smoothing occurs.

It does not produce errors of 50–100 ppm.

---

The paper never explains modern observations

Suppose the paper were correct.

Then we'd have to explain why:

• modern atmospheric CO₂ matches fossil-fuel emissions

• carbon isotopes identify fossil fuels as the source

• atmospheric oxygen is declining exactly as expected from combustion

• oceans are becoming more acidic as they absorb emitted CO₂

• satellites observe increasing infrared absorption by CO₂

Those independent observations all point to the same conclusion.

The paper does not address these lines of evidence.

---

The logic is backwards

Scientific reasoning normally works like this:

Measure CO₂.

Explain vegetation.

This paper instead says:

Estimate vegetation.

Infer CO₂.

Reject measurements if they disagree.

That's considerably weaker.

---

The references are selective

The bibliography relies heavily on a relatively small group of authors who frequently challenge mainstream climate science, while giving much less weight to the much larger body of paleoclimate research that supports the reliability of Antarctic ice cores. (ResearchGate)

That doesn't automatically invalidate the paper, but it should make readers cautious.

---

Does this disprove ice cores?

No.

To overturn decades of paleoclimate research, the paper would need to show that:

• Antarctic ice physically cannot preserve atmospheric CO₂,

• independent proxy records also fail,

• laboratory measurements of gas trapping are incorrect,

• and modern understanding of firn diffusion is wrong.

It does not do that.

Instead, it presents a model whose assumptions lead to a conflict with ice-core measurements and concludes the measurements must therefore be wrong. 

This paper doesn't present new measurements showing the ice cores are wrong. It starts with a model relating plant productivity to CO₂, assumes that similar greening in the past required much higher CO₂, and then concludes the ice cores must be inaccurate because they don't match the model. That's an indirect argument, not direct evidence. It also doesn't address the fact that multiple independent CO₂ proxies and modern atmospheric observations broadly agree with the ice-core record. Scientific evidence is strongest when independent methods converge on the same answer, and in this case they largely do.

 

Edited 9 hours ago by octave

[facthunter]

Even the OIL companies KNOW it's happening.. Plenty of deniers do so because it's in the Financial interests BHP lost a lot of face Recently and were caught out breaking a promise.. Trump and Hanson are Notable deniers but Hanson is a Trump Worshipper (and Farage and Victor Auban) Trump has also Handicapped the EPA.  Nev

[nomadpete]

The risk posed by relatively slight increases in  atmospheric temperature, is high.

 

A wet-bulb temperature (WBT) of 35°C  is the theoretical human survivability limit. This recently occured for six consecutive hours in July. Such conditions prevent evaporative cooling, rendering outdoor exposure potentially fatal without artificial cooling. Above 35 wbt, even lying down in the shade is fatal.

All biological systems have a range, and beyond that range the chemistry of life ceases. A body designed to operate with a core temp of 37C, can briefly sacrifice optimal performance to inhibit pathogen replication at 40c (fever), but will start failing, including seizures, at core temp of 41 or 42 c. 

 

If we get prolonged wbt over 35deg, the only humans that survive, will be those in A/C or underground.