The 0.1°C Challenge: The Heat on WMO-Compliant Temperature Sensors

Whether you’re tracking climate change, assessing floods, monitoring glacial retreat, or making critical decisions about aircraft landings, temperature data play a central role. Air temperature directly influences a wide range of atmospheric and environmental conditions, including humidity, pressure, and wind patterns. Accurate temperature measurements are essential not only for real-time decision-making, but also for long-term climate monitoring and scientific research.

But here's the catch: currently, different temperature sensors used globally create inconsistencies, which introduce questions about data accuracy, defensibility, and comparability.

In this blog article, we will explore Word Meteorological Organization (WMO) temperature standards, discuss the engineering challenges involved to comply with these guidelines, and highlight proven solutions that meet or exceed the requirements, raising the benchmark for temperature sensing around the world. 

The Challenge: Meeting WMO Temperature Recommendations

The United Nations’ WMO developed recommendations for various environmental and climate sensors, including temperature sensors. Historically, both engineering challenges and extraordinarily high costs were associated with trying to meet or exceed WMO temperature standards. Fortunately, recent advancements have made WMO-compliant measurements possible, accessible, and affordable.

Why do WMO compliance standards matter?

Accurate temperature data are foundational to a wide range of measurement systems, decisions, and policy-making processes. As the global climate continues to change, advancing climate science depends on high-quality data—data that are standardized, traceable, defensible, and accurate.

Unfortunately, around the world, sensor specifications for weather and climate data are highly variable, which makes it nearly impossible to create consistent and comparable numeric models from inconsistent data. Better data are needed for better forecasting models.

Because of the global need for high-quality data to feed high-quality models, the WMO established rigorous guidelines for environmental monitoring systems. Despite this, many commercially available temperature sensors have struggled to meet these standards.

For years, finding a temperature sensor that could deliver both low measurement uncertainty and a short time constant across broad temperature and wind ranges was virtually unattainable. This left researchers searching for solutions that could fulfill the WMO’s performance expectations—standards that represented serving the public good through better data.

Although WMO compliance is not mandated in all regions, their recommendations are widely regarded as the benchmark for temperature measurement quality. These guidelines represent a collaborative, global effort to create unified standards that enable temperature data to be accurate, defensible, comparable, and scientifically robust.

WMO compliance standards (found in WMO-No. 8¹ and summarized later in this article) are important for several reasons:

• Accuracy and Traceability – WMO-compliant sensors meet strict recommendations for accuracy, stability, and calibration traceability. In turn, this reduces measurement uncertainty, especially in extreme conditions.
• Global Data Comparability – WMO standards ensure that measurements taken across the globe are comparable and consistent. Without standardization methods and sensor specifications, temperature data from one station might not align with another, making it difficult to assess regional or global trends.
• Quality Control in Climate and Weather Records – Long-term climate datasets—often used to understand climate, validate models, or support policymaking—depend on high-quality, standardized observations. WMO compliance helps ensure the integrity and defensibility of these records.
• Designed for Real-World Conditions – WMO standards take into consideration real deployment factors to ensure environmental durability, not just lab conditions.

Ultimately, WMO compliance is about more than just a label. It’s about ensuring durability, dependability, and accuracy when measurements matter most.

What are the technical recommendations for WMO-compliant temperature sensors?

To be WMO compliant, temperature sensors must meet specific criteria, as found in WMO-No. 8, chapter 2. Here’s a summary:

After WMO-No. 8 was released, the WMO created a supplementary Instruments and Observing Methods Report, IOM 136, which further clarified their standards. IOM 136 defined the “achievable accuracy” tolerance for temperature measurements at ±0.2°C or better.² Achievable accuracy refers to the accuracy that can practically be achieved with high-quality instrumentation and procedures after external factors have been accounted for.

At the core of accurate temperature measurements is a sensor that meets or exceeds WMO-achievable accuracy recommendations. Even in well-managed installations, real-world factors can add onto small sensor inaccuracies and risk pushing the entire measurement outside of the acceptable ±0.2ºC tolerance. Because of this, carefully selecting sensors that meet or exceed the ±0.1ºC specification—especially when paired with a proper installation and use of a high-quality, compatible radiation shield—greatly increases the chance of meeting or exceeding the WMO IOM 136 recommendation for ±0.2ºC achievable uncertainty.

Sensors that Meet the Standard

Finding affordable, commercially available temperature sensors that meet or exceed WMO recommendations has long been a challenge. To address this gap, Campbell Scientific introduced two advanced sensor designs to achieve WMO compliance: the TempVue™10 and the TempVue™20.

Both TempVue models meet WMO standards as stand-alone sensors, offering measurement uncertainties of ±0.1°C across ranges of -80° to +60°C for the TempVue 10, and -40° to +40°C for the TempVue 20. These ranges cover nearly all ambient air temperatures typically encountered in global meteorological applications.

All TempVue models are delivered fully calibrated, with certification traceable to national standards. The accuracy level is made possible through key engineering choices, including minimizing thermal conductivity in the sensor body, isolating the platinum resistance thermometer (PRT) tip, and incorporating light-colored cabling to reduce radiative errors.

“The TempVue series sets a new standard in meteorological-grade temperature sensing,” said Chod Stephens, a technical product manager at Campbell Scientific.

Meeting WMO Standards for Time Constants in Stagnant Air

The time constant plays a vital role in air temperature measurements, whereby a shorter time constant allows sensors to respond more quickly to atmospheric changes, enhancing both performance and data quality.

As Dirk Baker, manager of Campbell Scientific’s Global Science Program, explained, “Air temperature is one of the most critical measurements for weather and climate. While scientists and manufacturers are continuously making improvements, there remain vital aspects where improvements are needed. One of these is how quickly a sensor responds to changes in the ambient conditions. This is quantified as the time constant.”

Baker added, “The sensors currently in use around the world vary widely in their time constant. Slower time constants lag behind changes in ambient temperatures, leading to error and uncertainty that can be substantial. These differences in time constant, error, and uncertainty further complicate comparing data across observation sites, networks, and historical data. The WMO recommends a time constant of 20 seconds or less. However, very few commercially available sensors for weather and climate meet this requirement.”

Most temperature sensors being used globally, regardless of type (liquid-in-glass, analog, digital, etc.) fail to meet or exceed WMO time constant recommendations in real-world wind conditions. In practice, this means that they are unable to detect rapid changes in ambient conditions, especially in stagnant or low wind conditions.

From "Improved time constant of a newly released air temperature sensor and its implications" (Burt and Baker, 2025). Used with publisher permission.
Click the graph for a larger image.

According to the peer-reviewed study Improved time constant of a newly released air temperature sensor and its implications,³ the TempVue 10 is among the first commercially available sensors that can meet, or exceed, the WMO’s time constant target of 20 seconds. The study’s authors, Burt and Baker, validate that the TempVue 10 (1.5 mm) sensor demonstrates a significantly shorter time constant compared to leading Stevenson-type sensors with larger diameter PRT tips (3 mm, 4.5 mm, and 6 mm).

Raising the Standard in Temperature Sensing

“Sensor providers should be raising the bar and holding ourselves to a standard where we can accurately measure 0.1°C or better temperature changes,” commented Stephens. As the demand for accurate, traceable, and standardized climate data grow, the importance of WMO-compliant temperature sensing can’t be overstated.

Whether you’re building a research-grade weather station or supporting long-term environmental monitoring, the sensor you choose must do more than just report a number; it must meet rigorous, globally recognized standards.

The TempVue 10 and 20 represent a new era of accessibility in high-precision meteorological measurement capability. With proven performance, calibration traceability, and adherence to WMO guidelines, they offer confidence in every degree—or tenth of a degree—you measure.

Learn more about our TempVue 10 Pt100 Analog Temperature Sensor or TempVue 20 Pt100 Digital Air Temperature Sensor.

Credits: Chod Stephens and Dirk Baker of Campbell Scientific, Inc. contributed to this article.

References

¹ World Meteorological Organization. (2025) Guide to instruments and methods of observation. Available from: https://library.wmo.int/records/item/68695-guide-to-instruments-and-methods-of-observation?offset=3.

² Body, D. and Kuik, F., (2021) Generic automatic weather station (AWS) tender specifications. Geneva: WMO.

³ Burt, S.D. and Baker, D.V. (2025) Improved time constant of a newly released air temperature sensor and its implications. Quarterly Journal of the Royal Meteorological Society, e4996. Available from: https://doi.org/10.1002/qj.4996.