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Articles by Andy May
Pages 2k Greenland Proxy Temperatures
By Andy May I’m reviewing the Pages 2k temperature proxies one-by-one as I once reviewed Marcott’s proxies (May, 2018). There are 647 Pages 2k proxies, so this is a big job. This reconstruction is prominently displayed and used in the IPCC AR6 report (IPCC, 2021, pp. 211, 432) so it is worth the time to investigate it. Their proxies can be downloaded as one R data file (RData format) from here.
What is the Best Human-Centric Climatic Baseline?
By Andy May The IPCC references global mean temperature increases to the 1850-1900 mean (IPCC, 2021, Ch. 2&4), and radiative forcing increases to 1750 (IPCC, 2021, Ch 7), then uses the two numbers to help them model warming since the pre-industrial period. According to Pages 2K the world warmed 0.1 to 0.2°C (see figure 1) between 1750 and 1850-1990 (Pages2K, 2019).
Deployable Energy’s new compact nuclear reactor
By Andy May I first read about Deployable Energy on Joanne Nova’s website and was very interested in their innovative small modular nuclear reactor and how it worked. The reactor was produced under President Trump’s 2025 nuclear reactor plan. It was designed by Australian Bobby Gallagher and his team in Houston. It can produce one megawatt of power, at a cost of 15 cents per kilowatt hour, for five years before refueling is required.
Comparing Equilibrium, Kinetic, and Non-Equilibrium Temperatures
By Andy May This is part 3 of a series on defining temperature. In part one I covered various temperature definitions used and pointed out that “temperature,” unmodified is only a measurement of an emergent statistical property with little meaning beyond that. It is important in physics and daily life, but not a primitive well defined property like mass or energy. In part two I covered kinetic temperature, which is “what we measure with a thermometer” (Schroeder, 2000).
Watts Up With That?
By Andy May In my last post, “Defining Temperature,” we saw that temperature is a simple measurement that has little meaning without context. If one is referring to the equilibrium system state variable or “thermodynamic equilibrium temperature,” they should state that to provide clarity because there are many types of temperature measurements and they mean different things. Thermodynamic equilibrium temperature is defined in the previous post.
Defining Temperature
I never thought I would participate in a serious debate on the definition of “temperature.” But it happened on twitter, and with people who have degrees in physics and other hard sciences! Since I worked with kinetic and effective temperature estimates for 42 years as a petrophysicist, I knew these topics intimately and never gave them a second thought. So, to hear people say (paraphrasing) that they were not really temperatures came as a shock.
Modeling the Troposphere
By Andy May and Philip Mulholland IGRA2 radiosonde 1991–2025 means (10 hPa bins, 10° latitude slices) show systematic differences between observed mid-tropospheric temperatures, and the CMIP 5 & 6 (Coupled Model Intercomparison Project, see IPCC, 2021) ensemble means as shown by McKitrick & Christy (2020) and Po-Chedley et al. (2022). The difference between the CMIP models and the observations is most noticeable in the tropics as discussed here.
Testing the Dew-Point Anchor Hypothesis
By Andy May and Philip Mulholland Earlier this year Philip Mulholland published the details of his Dew-Point Anchor Hypothesis or “DPAH” (Mulholland P. , 2026a). The hypothesis assumes that the Dew-Point Lifting Condensation Level (LCL), as calculated from surface conditions in the tropics, can act as an anchor for the lower and middle troposphere.
Do Los Niños cause climatic cooling?
By Andy May We’ve seen a lot of news stories about an upcoming El Niño, that may turn into a so-called “super” El Niño over the next year. This will affect our weather for a year or two, but what is the climatic effect of this weather feature, if any? Here we examine the history of warm ENSO events.
The Moist-Adiabatic Theory vs. Reality
By Andy May The moist‑adiabatic theory (Durran & Klemp, 1982) is one of the central organizing ideas in atmospheric thermodynamics, and it is used—both explicitly and implicitly—throughout modern climate models, especially in the tropics where it works best. It stems from thermodynamics and says that a rising parcel of humid air cools more slowly than a dry parcel because cooling causes condensation of water vapor which releases latent heat that warms the parcel.
Calculating Earth’s Albedo, Part 2
By Andy May It came up in the comments on my last post, CERES Albedo. What is the best way to compute Earth’s albedo? The CERES data is supplied as a 1° x 1° latitude/longitude grid. It is widely accepted that Earth’s global mean albedo is around 30%. The question is then: What is the best way to estimate it using the CERES satellite data? There are two basic ways.
Watts Up With That?
By Andy May Albedo (or Earth’s global reflectivity) in this post is defined as the amount of solar shortwave (SW) radiation that the Earth reflects into space, as measured at the top of the atmosphere or TOA, divided by the total solar radiation reaching Earth also measured at the TOA. In the CERES EBAF satellite context (Loeb et al., 2009, 2018, 2021), and using their variable names, this is toa_sw_all_mon divided by solar_mon, where “mon” means monthly and “sw” means shortwave radiation.
Earth Energy Imbalance: The Sun versus CO2
By Andy May This is the text of a talk I gave on a Tom Nelson podcast. To listen to the talk and see Tom’s interview of me go here. Some believe that CO2 and other greenhouse gas infrared emissions are as effective at increasing ocean heat content (or OHC) as solar radiation. Some even think greenhouse gas (abbreviated “GHG”) radiation is more effective than solar.
ECS, EffCS, and the 25-year Paradox, What CERES tells us
By Andy May The NCAR CERES EBAF satellite dataset has been adjusted to match upper ocean heat content changes. Thus, the EEI (Earth Energy Imbalance) from CERES EBAF (“Clouds and Earth’s Radiant Energy Systems, Energy Balanced and Filled”) is not estimated directly from satellite measurements. If upper ocean heat content were known accurately over a sufficiently long period, this would be fine, but it isn’t.
TOA EEI versus Surface Net Flux
By Andy May Fasullo & Trenberth (2008) build a closed, observation‑based annual energy budget for Earth’s climate system, partitioned into the top of the atmosphere (TOA), atmosphere, land, and ocean. They combine satellite radiation measurements, weather reanalyses, a stand‑alone land model, and several ocean temperature products.
Stefani on the Sun vs. CO2 as climate drivers
By Andy May Frank Stefani, of the Helmholtz-Zentrum Dresden-Rossendorf, Institute of Fluid Dynamics, has published a very interesting new paper that compares the solar “aa” index and CO2 emissions to global SST (sea surface temperatures using the HadSST4.2 dataset) and finds a CO2 sensitivity (TCR or the “Transient Climate Response”) of 1.1 to 1.4K. This is at the low end of the IPCC TCR range of 1.2 to 2.4K (IPCC, 2021, p.
Is the Ocean Surface a boundary condition?
By Andy May My previous post was a discussion about an important paper by Elizabeth Wong and Peter Minnett. The paper discusses the interaction between the thermal (or electromagnetic) skin layer (TSL) on the ocean and the bulk ocean. The TSL is only about 10 microns thick on average, although the thickness and temperature profile through it and under it changes throughout the day and night.
Efficacy of downwelling IR
By Andy May Solar radiation penetrates oceans to depths of 10-100 meters (depending on wavelength and water clarity), directly heating the ocean mixed layer. Greenhouse gas (GHG) infrared (IR), being longwave, is absorbed in the top ~10 microns (the thermal or electromagnetic skin layer or “TSL”), where it influences temperature gradients, evaporation, and conduction. The TSL lies on top of the mixed layer and has a different temperature.
The Neoglacial Period
By Andy May Most agree that the Milankovitch cycles of eccentricity, obliquity, and precession drive long-term global and hemispheric climate changes, see figure 4 in this post for a brief description of them. The modern climate debate is about short-term climate change. The “consensus” says that human emissions have caused “the most rapid change” or “temperatures are the warmest in X years” (Lecavalier et al., 2017) and (IPCC, 2021, p.
Holocene Glacier Records
By Andy May Glacier length changes through time, they advance when the local climate around them is colder and retreat when it is warmer (Bray, 1968). Over century and greater time scales glacier length is considered a highly reliable indicator of both regional and worldwide warming trends according to Olga Solomina, Johannes Oerlemans, and the IPCC (Solomina et al., 2008), (Oerlemans, 2005) & (IPCC, 2001, pp. 127-130).
Holocene Warming
By Andy May I find it amazing that some papers still state: “air temperatures in the [Arctic or globally] are now at their warmest in the past 6,800–7,800 y, and that the recent rate of temperature change is unprecedented over the entire Holocene.” (Lecavalier et al., 2017) While it is remotely possible that current Arctic or global average temperature is higher than any seen in the past 6,800 years, it is very unlikely and can’t be demonstrated with data we have today.
Re-evaluating the Concern of Climate Change
By Andy May I’ve just been made aware of a paper critical of the “consensus” view that man-made climate change is dangerous. It is by Ashutosh Sharma, Vinit Vithalrai Shenvi, and Mohit Sain of the MS Ramaiah Institute of Technology in India (or MSRIT) (Sharma et al., 2024). It was published just two months before “Carbon Dioxide and a Warming Climate are not problems,” by Marcel Crok and myself (May & Crok, 2024) and makes similar points, at least until we reach the paper’s conclusions.
The Cost of Wind and Solar Power Backup
By Andy May There have been many attempts to compare wind and solar power generation to generation with natural gas and other fossil fuels. I have summarized and criticized these attempts before, see here and here. Another excellent discussion of the topic is in this TPPF report by Michael Reed and Brent Bennet. Reed and Bennett estimate that modifying the Texas grid to handle wind and solar output variability cost Texas electricity consumers $2.3 billion in 2023.
Weather Reanalysis Models
By Andy May My new paper (May, 2025) emphasizes that while many of the underlying observations used to build weather reanalysis datasets, such as ERA5 (European Centre for Medium-Range Weather Forecasts or ECMWF Reanalysis v5) (Soci et al., 2024) or MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, Version 2) (Gelaro et al., 2017), are from radiosondes, weather reanalysis models are still models and have the same problems that other models have.
The Monthly ITCZ Central Latitude
By Andy May The Intertropical Convergence Zone or ITCZ is where the trade winds from the Northern and Southern Hemisphere converge and where the column-integrated meridional (north-south) circulation and the “near-surface meridional mass flux” vanishes according to Adam et al., 2016. For a history of the discovery of the ITCZ see Nicholson, 2018.
R Programming tips to process IGRA2 Radiosonde data
By Andy May In the last two posts (here and here) I showed how to read, plot, and map IGRA2 data. In this post I will discuss how to efficiently process large R data frames and lists to compute useful variables. One of the more difficult things to do in R is to write readable code. This problem has been around for a long time, but in recent years a very useful tool has appeared, the “pipe” or %>%. The %>% operator originates from the magrittr R package developed by Stefan Milton Bache in 2013/2014.
R Programming tips on mapping IGRA2 Radiosonde data
By Andy May Our last post was on reading and plotting IGRA2 weather balloon radiosonde data. This post shows how to map the data. The IGRA2 data can be downloaded from here (ftp site: ftp.ncei.noaa.gov/pub/data/igra). Once the data are prepared, some further tricky programming is needed to map it. This post will introduce the key concepts and code structure required. Writing complete programs will require understanding these concepts and working with Grok.
R Programming tips to read and plot IGRA2 Radiosonde data
By Andy May R is an extremely powerful programming language for processing, analyzing and displaying data from large datasets. As discussed in the first post of this series on analyzing IGRA2 radiosonde data with R, the language has improved considerably in recent years. Surprisingly it is free and can be downloaded here. This post will cover some necessary R programming techniques for those interested in reading and plotting IGRA2 data.
R Programming - Improvements in the Language
By Andy May This is an introductory post to a series on using R to read IGRA2 radiosonde data, process it, and produce both plots and maps of the data. I started using R over 10 years ago mainly because it was a free and very powerful language for statistical analysis (download the current 64-bit Windows version here). At the time, it was a clunky programming language and difficult to use, but that has recently changed.
The Story behind my Paper on the ITCZ and the Hadley Circulation
By Andy May It all began eight years ago when I read and reviewed Ronan and Michael Connolly’s first three papers on their ideas about the “molar density intersection” which is located just below the tropopause. I was quite fond of Michael Connolly, who sadly and suddenly passed away in August 2025, we all miss him.
What is a “climate crisis?”
By Andy May In a new paper by Gianluca Alimonti and Luigi Mariani, they argue that the public needs a proper definition of precisely what a climate crisis is to make rational decisions about how to address potential climate change threats (Alimonti & Mariani, 2025). They propose a set of measurable “Response Indicators” (RINDs) based on the IPCC AR6 Climate Impact drivers (IPCC, 2021, pp. 1851-1856). Their intent is to switch from subjective perceptions of possible dangers to quantifiable metrics.
‘Orwellian’ firing at the American Journal of Economics and Sociology for publishing a climate skeptic paper
By Andy May Well, it is official, Marty Rowland PhD has been fired from his position as Special Issue Editor at the American Journal of Economics and Sociology (AJES). The reason he was given for being fired was his publication of our paper, Carbon Dioxide and a Warming Climate are not problems. The paper has been cited 23 times according to google scholar. It was first published online May 29, 2024, and is already in the top 1% of all 29 million papers followed by Wiley’s Altmetric tracker.
Climate Oscillations 12: The Causes & Significance
By Andy May In this post we will examine the idea that ocean and atmospheric oscillations are random internal variability, except for volcanic eruptions and human emissions, at climatic time scales. This is a claim made by the IPCC when they renamed the Atlantic Multidecadal Oscillation (AMO) to the Atlantic Multidecadal Variability (AMV) and the PDO to PDV, and so on.
Climate Oscillations 11: Oceanic Niño Index (ONI)
By Andy May The Oceanic Niño Index or ONI is NOAA’s primarily indicator for monitoring the sea surface temperature (SST) anomaly in the critical Niño 3.4 region. It is a 3-month running mean of ERSST.v5 SST anomalies in the Niño 3.4 region, defined as 5°N-5°S and 120°W-170°W. Figure 1 shows the ONI as computed from the NOAA ERSST dataset. ERSST is a two-degree gridded dataset, so the region averaged for figure 1 is 6°N-6°S and 120°W-170°W.
Climate Oscillations 10: Aleutian Low - Beaufort Sea Anticyclone (ALBSA)
By Andy May The Aleutian Low – Beaufort Sea Anticyclone climate index or ALBSA is designed to compare the Aleutian Low Pressure and the Beaufort Sea High Pressure Centers. The intent is to relate air circulation patterns in the North Pacific and Arctic to climate and the timing of spring sea ice and snow melt.
Climate Oscillations 9: Arctic & North Atlantic Oscillations
By Andy May The Arctic Oscillation (AO) is closely related to the NAO (the North Atlantic Oscillation discussed below) but they are not the same. The NAO is usually measured using the SLP (sea level air pressure) difference between the Azores or the Iberian Peninsula and Iceland and is a North Atlantic regional phenomenon, whereas the Arctic Oscillation is the SLP difference between the northern mid-latitudes and the Arctic, and is evident in all longitudes (Thompson & Wallace, 2001).
Climate Oscillations 8: The NPI and PDO
By Andy May The North Pacific Index (NPI) is computed from the area-weighted sea level air pressure (SLP) over the region 30°N-65°N and 160°E-140°W. It measures interannual to multidecadal variations in Pacific atmospheric circulation. As explained in Trenberth and Hurrel, the winter Aleutian low pressure system moves on a decadal time scale and changes the climate and sea surface temperature (SST) along western North America and in the Northern Central Pacific.
Climate Oscillations 7: The Pacific Mean SST
By Andy May I originally planned to discuss the North Pacific Index (NPI) in this post, but while researching it, I discovered something interesting about Pacific sea surface temperature (SST) and how it relates to the HadCRUT5 global average surface temperature. As a result, this post is about the total Pacific mean SST and its correlation to HadCRUT5.
Climate Oscillations 6: Atlantic Meridional Mode (AMM)
By Andy May The Atlantic Meridional Mode Index (AMM) describes meridional variability in the tropical Atlantic. The area of interest is the ocean area inside 32°N to 21°S and from 75°W to the West African coastline (~15°E). Sometimes the boundaries are given as: 22°S-32°N and 74°W to the West African coast. This is the region where the Intertropical Convergence Zone (ITCZ) exists as it moves north and south with the seasons (Chiang & Vimont, 2004).
Climate Oscillations 5: SAM
By Andy May The Antarctic Oscillation (AAO) is also called the Southern Annular Mode or SAM. It is defined as the difference between the zonal (meaning east-west or circumpolar) sea level air pressure between 40°S and 65°S. That is the sea level pressure at 65°S is subtracted from the sea level pressure at 40°S (Gong & Wang, 1999).
Climate Oscillations 4: The Length of Day (LOD)
By Andy May In post 1, I ranked fourteen climate oscillations in Table 1 by their regression statistics against the HadCRUT5 global surface mean temperature. In this regression study the AMO is number one, the Western Hemisphere Warm Pool Area is #2, and the Northern Hemisphere sea ice area is #3.
Climate Oscillations 3: Northern Hemisphere Sea Ice Area
By Andy May Northern Hemisphere sea ice area is an important climatic indicator because it determines how much of the Arctic Ocean and surrounding seas are open to the atmosphere. Ice is a good insulator and traps heat in the water below it (Peixoto & Oort, 1992, p. 361). Ice is also a good reflector of sunlight (high albedo), whereas water is a good absorber (low albedo).
Climate Oscillations 2: The Western Hemisphere Warm Pool (WHWP)
By Andy May As seen in the first post of this series the AMO (Atlantic Multidecadal Oscillation) and the WHWP (Western Hemisphere Warm Pool) area are the two climate oscillations that explain most of the variability (64%) in the HadCRUT5 global mean surface temperature reconstruction (GMST) since 1950. Adding the Southern Annular Mode (SAM) explains 77% of HadCRUT5 variability.
Climate Oscillations 1: The Regression
By Andy May My last two posts, Musings on the AMO and The Bray Solar Cycle and AMO were fun to research and write, and they helped show that solar variations and cycles do have an impact on climate change regardless of what the IPCC says in AR6 WGI and their other reports. From AR6 WGI Chapter 7: “Changes in solar and volcanic activity are assessed to have together contributed a small change of –0.02 [–0.06 to +0.02] °C since 1750 (medium confidence).” (IPCC, 2021, p.
The Bray Solar Cycle and AMO
By Andy May My last post on the AMO and HadCRUT5 generated some interest and some criticism. As I explained, there are two common methods of computing the AMO index. One is to fit a least squares line to the AMO SSTs (sea surface temperatures in the North Atlantic) and use the line to detrend the AMO, creating an index. This was the original methodology as described by Enfield, et al. and Gray, et al.
Musings on the AMO
By Andy May We hear a lot about the AMO, or the Atlantic Multidecadal Oscillation. How much does it influence the global mean surface temperature or GMST? Exactly what is the AMO? These are the issues we will discuss. First let’s look at various definitions of the AMO.
Energy Consumption in 2024 and the Spanish Power Failure
What does the April 2025 Spanish power failure tell us about how we compare solar and wind to stable fossil fuel and nuclear power generation? By Andy May Global energy demand and consumption rose 2.2% in 2024 to a record high according to the 2025 IEA Global Energy Review released in March 2025. Growth in fossil fuel consumption accounted for 54% of the growing demand and growth in renewables and nuclear power accounted for the remainder. Most of the consumption growth was in emerging nations.
The Weather and Climate of World War II
By Andy May In my last post I discussed the evolution from the ICOADS raw sea surface temperature (SST) data to the final ERSST and HadSST SST anomalies. These anomalies are compared in figure 1. The ICOADS anomalies are generated by subtracting the 1961-1990 mean value from all the final raw simple yearly means. This was done last after the simple global mean SST had been computed for all years. The ERSST and HadSST values start out as anomalies.
What is the Global Average SST?
By Andy May The global average SST (Sea Surface Temperature) is a very important component of the global average surface temperature for the simple reason that the global ocean covers almost 71% of Earth’s surface. So, we downloaded the gridded SST data from 1850 through 2024 from the Hadley Centre (HadSST v4.1), NOAA (ERSST v5), and NOAA’s SST data repository (ICOADS v3) and then plotted the data in figure 1.
Plate Tectonics and Climate during the Cenozoic
By Andy May In this post I examine the proxies used to compare CO2 to temperature from 66 million years ago (Ma) until today and comment on the quality of the comparison. In addition, we look at the Cenozoic plate tectonic events that affected global climate. Figure 1 compares Westerhold et al.’s deep-sea d18O (the Oxygen-18 isotope anomaly, a temperature proxy) to the d13C (the Carbon-13 isotope anomaly), both measurements are from the same fossils, so they can be directly compared.
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