How do we measure greenhouse gases accurately across the entire planet — from the surface we stand on to 800 km above Earth? And how can we ensure that these measurements, taken with different instruments in different conditions, remain comparable and trusted over time?

At the BIPM’s Scientific Conference during the 150th Anniversary of the Metre Convention, Dr Mahesh Kumar Sha of the Royal Belgian Institute for Space Aeronomy (BIRA-IASB) spoke with the BIPM about how different observing techniques work together to build a reliable picture of our atmosphere.

Watch our interview

In this short video, Dr Sha explains how satellites measure reflected sunlight from the Earth's surface and the scattered radiation in the atmosphere to retrieve greenhouse-gas concentrations, why factors such as surface albedo, aerosols and humidity introduce uncertainties, and how ground-based reference networks help validate satellite data and correct biases.

These measurements underpin more accurate emission estimates and support emerging systems such as the WMO Global Greenhouse Gas Watch (G3W).

[4 minutes]

Watch Dr Sha's Keynote Address

In his #BIPM150 keynote address, Dr Sha explores the wider landscape of greenhouse-gas observations — from surface and airborne measurements to satellite missions — and shows why fiducial reference measurements (FRM) are essential for ensuring that spaceborne data remain accurate, traceable and globally comparable.

He also describes how portable Fourier transform infrared (FTIR) instruments, characterized at reference sites and deployed as travelling standards, can help strengthen coverage in data-sparse regions.

[25 minutes]