I don't think anyone saying this has really looked at how that determination is made so I looked into it some.

First, let's look at the baseline they use to make that determination

quote:
Indeed, the warming continues. The 10-year average for the period 2013-2022 is estimated to be 1.14 [1.02 to 1.27] °C above the 1850-1900 pre-industrial baseline. This compares with 1.09°C from 2011 to 2020, as estimated by the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment report.

World Meteorological Organization

The problem with using 1850 to 1900 as a baseline is their data is junk or nonexistent. Since it was nonexistent they acknowledge it is mostly estimations based on what little data they do have.

quote:
Three of the world’s most complete temperature tracking records – from NASA’s Goddard Institute for Space Studies, the National Oceanic and Atmospheric Administration’s National Climactic Data Center and the UK Meteorological Office’s Hadley Centre – begin in 1880. Prior to 1880, temperature measurements were made with instruments like thermometers. The oldest continuous temperature record is the Central England Temperature Data Series, which began in 1659, and the Hadley Centre has some measurements beginning in 1850, but there are too few data before 1880 for scientists to estimate average temperatures for the entire planet. Data from earlier years are reconstructed from proxy records like tree rings, pollen counts, and ice cores. Because these are different kinds of data, scientists generally don’t put proxy-based estimates on the same charts as the “instrumental record.”

The above-mentioned agencies and others collect temperature data from thousands of weather stations worldwide, including over the ocean, in Antarctica, and from satellites. However, instruments are not perfectly distributed around the globe, and some measurement sites have been deforested or urbanized since 1880, affecting temperatures nearby. Each agency uses algorithms to filter the effects of these changes out of the temperature record and interpolate where data are sparse, like over the vast Southern Ocean, when calculating global averages.

NASA

Even the U.S. Historical Climatology Network has changed several times how they quantify national and regional-scale temperature changes. When was the most recent change? 2012

quote:
Version 2.5 was released as a revision to the version 2.0 dataset In October 2012. The processing steps for version 2 and 2.5 are essentially the same, but the version number change reflects modifications to the underlying database as well as coding changes to the pairwise homogenization algorithm (PHA) that improve its overall efficiency. Table 1 (below) lists these modifications. NCEI Technical Reports GHCNM-12-01R (Williams et al., 2012a) and GHCNM-12-02 (Williams et al. 2012b) provide details regarding the PHA modifications.

Version 2 monthly temperature data incorporated an expanded database of raw temperature values from COOP stations, a new set of quality control checks, and a more comprehensive homogenization algorithm. The version 2 temperature dataset and processing steps detailed description are in Menne et al. (2009).

Version 1 is made up of three dataset releases (described in Quinlan et al. 1987, Karl et al., 1990 and Easterling et al., 1996). These datasets contained adjustments to the monthly mean maximum, minimum, and average temperature data that addressed potential documented in NCEI’s station history archives. The documented changes that were addressed include changes to the time of observation (Karl et al. 1986), station moves, and instrument changes (Karl and Williams, 1987; Quayle et al., 1991). Apparent urbanization effects were also addressed in version 1 with a specific urban bias correction (Karl et al. 1988).

In 2007, USHCN version 2 serial monthly temperature data were released and updates to the version 1 datasets were discontinued.

LINK

The original version was built on the old data previously mentioned. They refer to it as COOP stations

quote:
The National Weather Service (NWS) Cooperative Observer Program (COOP) is a network of daily weather observations taken by more than 8,500 volunteers. These data, which include observations from the late 1800’s, are vital to understanding the U.S. climate, and also provide near real-time information that supports forecasts, warnings and alerts, and other public service programs. Observations taken from around the U.S. and its territories at National Parks, seashores, mountaintops, farms, and many urban and suburban areas. COOP data usually consist of daily maximum and minimum temperatures, snowfall, snow depth, and 24-hour precipitation totals. Observations may include additional hydrological or meteorological data such as evaporation or soil temperatures.

noaa.gov

Again when you look at this you have to take into account that they have admitted data prior to 1900 was mostly estimations based on what little data they do have

Now let's look at the number of weather stations worldwide over the years.

quote:
This data set contains monthly temperature, precipitation, sea-level pressure, and station-pressure data for thousands of meteorological stations worldwide. The database was compiled from pre-existing national, regional, and global collections of data as part of the Global Historical Climatology Network (GHCN) project, the goal of which is to produce, maintain, and make available a comprehensive global surface baseline climate data set for monitoring climate and detecting climate change. It contains data from roughly 6000 temperature stations, 7500 precipitation stations, 1800 sea level pressure stations, and 1800 station pressure stations. Each station has at least 10 years of data, 40% have more than 50 years of data. Spatial coverage is good over most of the globe, particularly for the United States and Europe. Data gaps are evident over the Amazon rainforest, the Sahara Desert, Greenland, and Antarctica.

LINK

Less than half have more than 50 years of data

Here is the progress of those 7500 rain gauges over the decades 6000 of which are also temperature stations

>

LINK

2017 is the peak of all stations and since 2015 we have been claiming the past 8 years (including this one) are the hottest on record

No doubt with the advancement of technology and more stations we are able to measure temperatures more accurately than at any time in history. The problem with this new data is that we are comparing it to estimates from the 1800s as a baseline despite the fact that less than half of all stations have more than 50 years of data.

Have the last 8 years really been the hottest on record or are they just the most accurately measured years in history?